UC-NRLF 


GIFT   OF 


THE 

SECRET   OF   EXPOSURE 


Practical  Photography,  No.  I 


EDITED    BY 


FRANK  R.  FRAPRIE,  S.  M.,  F.  R.  P.  S. 

Editor  of  AMERICAN  PHOTOGRAPHY  and  POPULAR  PHOTOGRAPHY 


ELEVENTH  THOUSAND 
REVISED  AND  ENLARGED 


American  Photographic  Publishing  Co. 

Boston,    Mass. 

1915 


~TfC  *•'  / 


Copyright,  1906,  by  F.  DUNDAS  TODD 
Copyright,  1911,  1913,  I9U,  by  F.  R.  FRAPRIE 


Copyright,  1912,  1915, 

by 
AMERICAN  PHOTOGRAPHIC  PUBLISHING  Co. 


Stanbopc  flbress 

F.    H.GILSON   COMPANY 
BOSTON,  U.S.A. 


THE 

SECRET  OF  EXPOSURE. 


Introductory.  —  The  first  roll  of  films  teaches  the 
beginner  with  the  camera  that  there  is  an  exposure 
problem  to  be  met  and  mastered.  If  he  be  sufficiently 
interested  to  go  over  the  negatives  at  the  supply  shop 
with  the  clerk,  the  latter  points  out  to  him  that  this 
one  is  not  good  because  it  did  not  receive  enough 
exposure;  that  one,  because  it  had  too  much;  while 
the  other  is  properly  timed  and  gives  a  satisfactory 
print.  Often,  however,  the  results  seem  so  good  to 
the  novice  that  he  is  delighted  and  goes  ahead  with 
the  work  without  stopping  to  learn  how  to  regulate 
exposure,  and  it  is  later,  when  bad  results  come  thick 
and  fast,  that  the  awakening  comes.  At  this  stage, 
unfortunately,  for  want  of  proper  help,  many  ama- 
teurs shelve  the  camera  in  disgust.  Others  —  those 
whom  we  are  addressing  —  refuse  to  be  vanquished 
and  ask  to  be  shown  how  to  master  the  all-important 
secret  of  exposure. 

Vacation  Snapshots.  —  So  long  as  the  camera  is 
used  only  for  the  ordinary  kinds  of  snapshots  turned 
out  by  millions  during  the  summer  months,  failures 
are  not  likely  to  occur.  The  manufacturers  of  even 
the  lowest-priced  cameras  have  provided  lenses  well 

3 


J  SECRET   OF   EXPOSURE. 


fitted  to  give  good  results  in  intense  summer  sunshine 
with  the  snap  of  about  1-25  second  which  the  shutter 
will  make.  This  exposure,  1-25  second  with  stop 
/:i6,  is  not  enough,  however,  before  9  A.M.  or  after 
3  P.M.  One  of  the  most  usual  failures  which  be- 
ginners make  is  due  to  their  attempting  snapshots 
very  late  in  the  afternoon,  when  the  light  is  still  bright 
to  the  eye  but  not  capable  of  affecting  the  film  suffi- 
ciently. The  only  remedy  in  such  circumstances  is 
to  calculate  the  exposure  by  means  of  tables  or  a  meter 
and  use  a  smaller  stop  or  opening  in  the  lens  with  a 
short  "  time  "  exposure.  This,  of  course,  necessitates 
a  tripod  or  other  firm  support  to  prevent  the  camera 
from  moving  and  thus  blurring  the  picture  while  the 
lens  is  open. 

Limits  of  the  Cheap  Cameras.  —  Assuming  that  the 
beginner  is  equipped  with  a  "  fixed-focus  "  camera 
fitted  with  meniscus  achromatic  lens  working  at  /:i6 
and  a  shutter  giving  1-25  second  and  time  exposures, 
exposures  within  the  range  of  the  combination  will 
be  found  to  lie  pretty  sharply  within  the  hours  named 
above.  Snapshots  in  the  shade,  unless  there  is  a  flood 
of  reflected  light,  will  fail.  So  will  those  made  too  far 
from  noon,  on  a  dull  day  without  sunlight,  of  objects 
very  close  to  the  lens,  as  bust  portraits  (except  in 
direct  sunlight),  and  in  narrow  city  streets.  Similarly, 
failure  will  follow  the  making  of  snapshots  on  the 
water;  but  in  this  case  from  overexposure.  Sky  and 
sea  are  so  very  brilliant  that  they  affect  the  film  too 
much.  The  use  of  a  smaller  opening  or  stop  in  the 
lens  with  the  same  speed  of  snapshot  is  the  way  to 
overcome  this  fault,  as  the  smaller  hole  admits  less 
light  during  the  same  duration  of  exposure. 


THE   SECRET   OF   EXPOSURE.  5 

Increased  Latitude  of  Better  Cameras.  —  From 
what  has  just  been  said,  it  is  easy  to  deduce  the  fact 
that  regulation  of  exposure  is  made  more  easy  and 
certain  if  we  have  the  power  to  change  both  the  lens 
opening  and  the  shutter  speed.  Hence  if  a  camera 
is  fitted  with  a  double  or  rapid  rectilinear  lens,  we  have 
a  greatly  augmented  range.  Instead  of  a  largest 
stop  of  /:i6,  we  have  one  of  /:8,  which  admits  four 
times  as  much  light.  We  have,  generally,  several 
speeds  of  snapshot,  such  as  i-ioo,  1-50,  and  1-25 
second.  By  paying  more,  we  can  get  speeds  running 
from  time  and  bulb  to  automatically-regulated  slow 
exposures  of  I,  1—2,  and  1—5  second  (all  too  slow  to  use 
unless  the  camera  is  placed  on  a  tripod)  and  snapshots 
as  fast  as  an  actual  1-250  or  1-300  second.  It  is, 
notwithstanding,  hardly  worth  while  to  pay  the  top 
price  for  a  shutter  provided  with  so  many  speeds 
unless  one  also  secures  in  it  a  fast  anastigmat  lens, 
which  will  open  wider  than  /:8.  One  working  at  /:6 
to /:6. 8  will  be  found  most  suitable  for  general  amateur 
work.  The  combination  of  a  rapid  lens  with  the 
many-speeded  shutter  will  allow  one  to  make  snap- 
shots early  or  late  in  the  day,  in  the  shade,  or  on  dull 
days,  and  succeed  admirably,  if  the  correct  exposure 
is  known  in  advance  and  secured  by  regulation  of  the 
stop  and  the  shutter  speed. 

Necessity  of  Information.  —  To  expose  correctly, 
then,  it  is  requisite  that  the  camera  user  study  his 
instrument  and  the  various  factors  which  control  the 
length  of  exposure  and  become  thoroughly  familiar 
with  all  the  facts  which  can  be  brought  to  his  aid. 

The  Problem.  —  All  objects  in  nature  reflect  light 
to  the  eye.  If  the  amount  of  light  reflected  is  great, 


THE  SECRET  OF  EXPOSURE. 


I'ig.  i.  —  Underexposure.    Also  illustrating  a  Street  Scene 

as,  for  example,  that  thrown  back  by  a  sheet  of  white 
paper  in  sunlight,  we  call  the  paper  a  highlight.  A 
piece  of  black  velvet  in  shadow  reflects  very  little  light 
and  is  called  a  shadow.  The  tones  between  these 
extremes  are  called  halftones.  As  a  general  thing, 
most  photographs  represent  from  four  to  six  separate 
tones  between  pure  white  paper  and  the  blackest 
shadows.  For  the  sake  of  simplicity,  let  us  take  a 
wooden  block  painted  white  and  set  it  in  front  of  a 
black  background  and  light  it  so  that  the  white  paint 
shall  show  to  the  eye  three  distinct  tones  —  pure  white 
and  two  intermediate  grades  of  halftones.  The  black 
background  forms  the  shadow,  or  fourth  tone.  Our 
task  is  to  take  a  photograph  which  shall  accurately 
represent  these  four  tones  as  they  look  to  the  eye. 
The  human  organs  of  vision  accommodate  themselves 
almost  at  once  to  the  light  illuminating  the  object  and 
the  brain  records  a  conception  which  does  not  change 
according  to  the  length  of  time  the  block  is  viewed. 
In  other  words,  it  looks  the  same  whether  we  gaze  at 
it  for  a  second  or  for  a  minute.  With  the  photo- 


THE  SECRET  OF   EXPOSURE. 


Fig.  2.  —  Correct  Exposure.    Also  Illustrating  Average 
Landscape 

graphic  plate,  on  the  contrary,  it  is  far  otherwise. 
The  exposure,  or  length  of  time  the  light  is  allowed 
to  act,  must  fall  within  very  narrow  limits  or  the 
result  will  be  untrue  to  our  visual  impression.  To 
understand  this  fully,  let  us  briefly  review  the  action 
of  light  on  the  plate  or  film. 

Action  of  Light  on  the  Plate.  —  The  emulsion  of 
the  plate  consists  of  innumerable  small  particles  of 
silver  bromide  imbedded  in  gelatine.  Each  of  these 
tiny  bits  of  solid  matter  is  capable  of  being  altered 
when  light  strikes  it,  so  that,  although  it  shows  no 
visible  change,  it  will  blacken  and  become  a  minute 
grain  of  metallic  silver  when  acted  on  by  the  developer. 
A  definite  minimum  amount  of  light  is  needed,  and 
this  quantity  becomes  a  measure  of  the  speed  of  the 
plate.  Anything  less  than  this  intensity  of  light  does 
not  act  enough  on  the  particle  and  is  called  under- 
exposure. (Fig.  I.)  If  the  light  acts  for  just  the 
right  time,  the  number  of  particles  affected  and 
blackened  in  development  is  such  that  the  tones  form 
a  negative  record  of  the  tones  of  the  object,  being 


THE  SECRET  OF   EXPOSURE. 


M.  D.  Miller 

Fig.  3.  —  Extreme  Overexposure,  with  Reversal  of  the 
.    Sun's  Disc 

black  or  opaque  where  the  object  is  white,  and  trans- 
parent where  the  black  occurs  in  the  shadow.  With 
such  a  correct  exposure  (Fig.  2),  which,  in  the  case  of 
a  good  plate,  may  extend,  let  us  assume,  from  I  to  5 
units  of  time,  the  tones  are  properly  rendered  and  the 
print  from  the  negative  looks  about  as  the  object  does 
to  the  eye.  Beyond  this  arbitrary  limit  of  5,  however, 
the  increase  of  exposure  affects  more  particles  of  silver 
bromide  than  are  needed,  and  these  blacken  in  de- 
velopment and  cause  the  negative  to  look  flat.  (Fig. 
3.)  This  is  overexposure.  The  shadows  have  too 
much  detail  and  print  gray  instead  of  black;  the  half- 
tones are  as  opaque  as  the  highest  lights  and  also  print 
gray.  There  is  no  contrast  between  the  tones.  If 
one  carries  the  process  far  enough,  say  several  thou- 
sand times  normal,  the  highlights  become  thinner 
and  thinner,  the  shadows  more  and  more  opaque, 
until  at  last  the  image  becomes  positive  instead  of 
negative.  This  phenomenon  is  known  as  reversal 
of  the  image  (Fig.  3  shows  reversal  of  the  sun),  and 


THE  SECRET   OF  EXPOSURE.  9 

occurs  with  all  plates,  except  those  prepared  with 
hydrazine  and  marketed  under  the  trade  name  of 
"  Hydra  "  by  an  English  firm.  In  these,  the  chemi- 
cal named  hydrazine  prevents  reversal  and  allows 
exposure  of  almost  any  duration  to  be  given  with- 
out the  necessity  of  losing  the  plate  from  overex- 
posure. 

Correct  Exposure.  —  To  solve  our  problem,  then, 
we  must  find  the  exposure  between  I  and  5  —  the 
"  latitude  "  of  a  good  plate  or  film  —  and  then  our 
negative  will  correctly  represent  the  difference  be- 
tween the  tones  as  seen  by  the  eye.  As  different 
brands  vary  in  sensitiveness  to  light,  it  is  necessary 
to  have  some  standard  by  which  to  compare  them. 
This  is  found  in  the  H.  and  D.  numbers  when  all 
brands  are  exposed  to  the  same  standard  light  and 
developed  with  the  same  developer;  but  since  no 
two  makers  employ  identical  materials  and  methods 
it  is  not  possible  to  compare  one  maker's  H.  and  D. 
speed  numbers  with  those  of  another  maker. 

How  H.  and  D.  Speeds  are  Found.  —  The  ex- 
posure apparatus  of  Hurter  and  Driffield  consists 
essentially  of  a  rotating  sector  disc  which  revolves 
in  front  of  the  plate  and  exposes  it  in  bands  so  that 
the  exposures  of  the  different  bands  are  in  geometri- 
cal ratio.  An  exposure  of  convenient  duration  is 
given,  and  the  plate  is  then  developed  in  a  standard 
developer  for  a  certain  time  at  a  certain  tempera- 
ture. The  fixed  negative  shows  a  series  of  strips 
extending  from  the  faintest  deposit  of  silver  (under- 
exposure) to  maximum  density  and  beyond  this  to 
beginning  reversal.  It  is  then  placed  in  another 
piece  of  apparatus  in  which  the  densities  of  the  de- 


10 


THE  SECRET  OF  EXPOSURE. 


I 


Scale    of  log  exposures 

Fig.  4.  —  A  Typical  H.  &  D.  Curve 

posits  are  read  off  and  the  results  are  plotted  out  on 
co-ordinate  paper,  the  densities  as  ordinates  or  vertical 
distances,  and  the  logarithms  of  the  exposures  as 
abscissae  or  horizontal  distances.  See  Fig.  4. 

The  first  part  of  the  curve,  a  to  b,  is  concave  upward 
and  represents  the  period  of  underexposure.  The 
straight  portion  of  the  curve,  b  to  c,  is  the  period  of 
correct  exposure,  or  latitude,  and  exposures  anywhere 
within  the  limits  traced  by  the  straight  line  will  give 
good,  printable  negatives,  with  accurate  differentia- 
tion between  the  tones,  though  the  general  opacities 
or  densities  will  increase  with  added  exposure.  That 
is,  if  the  correct  exposure  extends  from  I  to  5,  the 
negative  given  5  will  be  denser  throughout  than  that 
given  i,  but  the  relations  between  the  different  tones 
will  be  the  same,  though  the  times  needed  to  take 
off  a  print  are  widely  different.  The  moment,  how- 
ever, exposures  in  excess  of  5  are  given  the  period  of 
overexposure  begins,  the  straight  line  becomes  a  curve, 
c  to  d,  and  reaches  a  summit  only  to  drop  rapidly 
away,  the  last  portion  being  omitted  in  our  cut.  The 


THE  SECRET  OF   EXPOSURE.  n 

density  of  the  deposit  of  silver  lessens  because  of 
reversal,  as  the  grains  of  silver  bromide  which  have 
received  excessive  light  action  are  no  longer  reduced 
fully  and  some  are  not  reduced  at  all.  The  latter 
remain  in  the  yellow  state  and  the  plate  is  said  to  be 
solarized.  Fixing  removes  the  unaltered  bromide  and 
the  highlights  are  thinned  in  proportion  to  the  over- 
exposure.  This  property  of  partial  reversal  of  the 
highlights  is  a  most  useful  one,  as  we  shall  see  later; 
but  now  let  us  see  the  end  of  our  H.  and  D.  curve. 
The  straight  portion  of  the  curve  is  produced  until 
it  cuts  the  base  line  at  e,  and  the  value  found  at  this 
point  is  called  the  inertia  of  the  plate.  The  greater 
the  inertia,  the  slower  the  plate.  The  speed  of  the 
plate,  or  H.  and  D.  number,  is  found  by  dividing  34 
by  the  inertia.  This  value  is  also  often  called  the 
actinograph  number,  as  it  is  used  with  a  calculator 
sold  abroad  under  the  name  of  the  actinograph. 
From  the  true  H.  and  D.  number  the  Watkins  and 
Wynne  speed  numbers  are  calculated. 

At  this  point  it  may  be  as  well  to  emphasize  the 
fact  that  most  makers  of  plates  do  not  follow  the 
standard  conditions  laid  down  by  the  original  in- 
vestigators, owing  to  differences  of  opinion  among 
scientists  as  to  standard  lights,  or  for  other  reasons. 

Independent  Standards.  —  Watkins  numbers  can 
be  relied  on,  because  the  Watkins  Meter  Company  is 
in  an  absolutely  independent  position  and  has  no 
interest  in  overstating  the  speeds  —  a  temptation 
which  has  led  some  of  the  platemakers  to  exaggerate, 
or  to  adopt  some  modification  of  the  H.  and  D.  method 
of  speed  testing  which  shall  give  very  high  readings. 
For  example,  some  firms  give  H.  and  D.  numbers 


12  THE   SECRET   OF   EXPOSURE. 

which  are  very  low,  and  the  Watkins  speed  has  to  be 
found  by  multiplying  them  by  I J  or  even  by  2  —  the 
method  used  by  the  Watkins  people.  Other  makers, 
on  the  contrary,  claim  H.  and  D.  numbers  much 
higher  than  the  correct  Watkins  ratings.  The  first 
may  list  a  plate  as  H.  and  D.  125;  the  second  may 
rate  a  plate  of  exactly  the  same  speed  as  H.  and  D. 
400.  In  fact,  one  cannot  rely  at  all  on  H.  and  D. 
numbers  as  used  by  platemakers.  On  tire  other  hand, 
one  may  think  the  Watkins  numbers  err  on  the  side 
of  conservatism;  but  when  all  is  said,  one  is  more 
liable  to  lose  a  plate  through  undertiming  than  any 
other  error  whatsoever,  so  it  is  a  positive  advantage 
to  know  what  good,  full  exposure  is.  It  is  easy  to 
give  less,  if  desired;  but  it  is  impossible  to  bring  out 
in  development  any  details  which  have  not  been 
sufficiently  exposed.  Hence,  if  any  reader  thinks  the 
exposures  we  recommend  (calculated  by  the  Tables 
given  herewith,  or  by  the  published  Watkins  or  Wynne 
numbers)  are  too  great,  let  him  stick  to  the  published 
speed  rating  and  simply  give  a  shorter  time,  as  experi- 
ment and  his  personal  taste  may  dictate.  The 
writer's  own  allowance  outdoors  for  average  land- 
scapes is  half  the  full  Watkins  Bee  meter  time,  to 
compensate  for  the  high  efficiency  of  an  expensive 
shutter  having  accurate,  tested  speeds.  Indoors,  the 
full  time  is  given.  A  similar  allowance  may  be  made 
from  the  Table  times  without  getting  serious  under- 
exposure. 

Equivalent  Plate-speed  Numbers.  —  The  follow- 
ing table  indicates  the  corresponding  speeds  of 
different  systems. 


THE  SECRET   OF   EXPOSURE. 


A.  P. 

Watkins. 

Wynne. 

A.  P. 

Watkins. 

Wynne. 

\ 

500 

FiS6 

5^ 

16 

F  28 

I 

350 

F  128 

6 

II 

F22 

I* 

250 

F  in 

6| 

8 

F20 

2 

1  80 

F    90 

7 

6 

Fi6 

2| 

130 

F    78 

7* 

4 

Fi4 

3 

90 

F    64 

8 

3 

Fn 

3l 

65 

F    56 

8| 

2 

F  10 

4 

45 

F    45 

9 

3 

4 

F    9-5 

4* 

32 

F    39 

9i 

I 

F    8 

5 

22 

F    32 

Correct  Exposure  and  Printing  Quality.  —  As  we 
have  seen,  correct  exposure  is  a  variable  quantity 
extending  from  a  minimum  useful  amount  to  one 
several  times  as  great.  The  statement  of  the  case 
in  the  words  of  Mr.  Vero  C.  Driffield*  may  be  of 
assistance.  "  I  have  in  my  possession  two  negatives 
of  the  same  subject  taken  upon  the  same  plate  and 
developed  together  for  the  same  length  of  time,  but 
the  latitude  of  the  plate  used  was  such  as  to  permit 
of  one  negative  being  exposed  for  ten  times  as  long 
as  the  other.  While  one  of  the  negatives  has  every 
indication  of  a  perfect  exposure,  the  other  gives  to  the 
eye  the  impression  of  heavily  fogged  overexposure ; 
yet  they  yield  identical  prints.  The  time  occupied  in 
printing,  however,  while  quite  normal  in  one  case, 
amounts  to  two  or  three  days  in  the  other.  My  object 
in  mentioning  this  is  to  point  out  that  a  photographer 
who  might  inadvertently  produce  such  a  negative  as 
the  denser  of  these,  would,  from  its  behavior  in  the 
developer,  probably  conclude  that  he  had  enormously 
overexposed.  He  would  at  once  stop  development, 


*  The  Photo-Miniature,  No.  56,  page  385. 


14  THE   SECRET   OF   EXPOSURE. 

reconstitute  his  developer,  and,  on  taking  a  print  from 
the  finished  negative,  flatter  himself  that  the  result 
was  due  to  his  skill  in  development,  while,  as  a  matter 
of  fact,  the  gradations  of  his  negative  were  true  from 
the  outset.  In  the  instance  referred  to,  the  image  of 
the  denser  negative  flashed  up  in  the  developer  far 
more  rapidly  than  that  of  the  other,  and  by  the  time 
development  was  completed  it  was  lost  in  an  ap- 
parently impenetrable  deposit  of  high  density.  From 
this,  it  is  obvious  that  a  system  of  timing  development 
by  the  first  appearance  of  the  image  is  fallacious;  and, 
had  it  been  resorted  to  in  this  instance,  the  two  nega- 
tives would  never  have  yielded  identical  prints.  When 
two  negatives,  such  as  those  described,  yield  identical 
prints,  their  density  differences  are  alike  throughout, 
though  the  density  ratios  differ." 

Why  the  H.  and  D.  Numbers  must  be  Checked  by 
Test.  —  It  has  always  been  evident  that  speed  num- 
bers found  by  any  artificial-light  test  must  be  corrected 
by  actual  trial  for  daylight  exposures.  The  difficulty 
is  largely  due  to  the  color-sensitiveness  (or  lack  of  it) 
of  different  emulsions,  so  that,  for  instance,  an  ortho 
plate  may  give  an  absurdly  low  H.  and  D.  number  and 
its  speed,  for  practical  purposes,  has  to  be  determined 
by  camera  exposures.  The  necessary  correction  is  made 
by  the  authors  of  speed  lists,  who  convert  the  true  H. 
and  D.  number  to  their  own  system  and  prove  its 
correctness  by  camera  exposures  outdoors.  The  plate 
number,  in  any  system,  may  be  regarded  as  the 
regulator,  to  be  set  faster  or  slower  by  the  user  to  suit 
his  own  particular  notions  of  just  what  exposure  he 
wishes.  Something,  of  course,  depends  on  the  de- 
velopment, and  we  cannot  too  strongly  urge  the 


THE  SECRET   OF   EXPOSURE.  15 

standardization  of  this  element  by  the  use  of  the 
Thermo  system  of  development,  by  means  of  which 
all  variations  in  temperature,  etc.,  may  be  compen- 
sated for  very  exactly  and  a  standard  amount  of 
contrast  between  the  tones  always  be  obtained  with 
precision.  The  system  is  described  in  full  in  The 
Watkins  Manual  (price  60  cents,  from  our  publishers), 
and  suitable  tables  are  furnished  by  us  in  card  form 
for  darkroom  use  for  25  cents. 

Another  reason  for  checking  speeds  by  trial  is  that 
practically  all  of  the  ultra-rapid  plates  (our  Class  J) 
are  abnormal  in  their  characteristics,  as  compared  to 
slower  emulsions.  They  are  intended  chiefly  to 
utilize  the  underexposure  portion  of  the  H.  and  D. 
curve,  and  it  will  be  found  that  when  the  lowest  tones 
(clear-glass  shadows)  fall  very  close  to  the  point  where 
no  light  action  can  be  demonstrated,  the  highlight 
details  come  rather  low  on  the  straight-line  portion 
and  give  printable  differences.  If,  on  the  other  hand, 
these  plates  are  given  normal  exposures,  so  as  to  bring 
the  whole  exposure  on  the  straight-line  portion,  the 
upper  tones  suffer  from  "  plugging  up,"  that  is,  there 
are  no  printable  differences  between  them.  In  prac- 
tice, then,  one  finds  that  when  these  plates  are  used 
they  must  be  very  judiciously  timed,  avoiding  any 
suspicion  of  overtime,  and  developed  in  a  very  con- 
centrated solution.  In  speed  work,  particularly,  with 
exposures  of,  say,  1-250  second  with  a  Compound 
shutter  or  1-600  and  1-1200  with  a  focal-plane  shutter, 
the  necessary  general  density  for  printing  quality  can 
only  be  obtained  by  special  methods  of  development, 
such  as  the  use  of  concentrated  developer  or  a  greatly 
prolonged  time  of  development,  not  to  mention  special 


16  THE   SECRET   OF   EXPOSURE. 

formulae  designed  to  stain  the  plate  and  thereby 
increase  the  non-actinic  nature  of  the  silver  deposit. 
Speed  work,  however,  is  abnormal,  for  the  first  con- 
sideration must  be  to  use  a  shutter  speed  high  enough 
to  "  stop  motion  "  and  the  second  is  to  make  the  most 
of  a  known  underexposure. 

Watkins'  Central  Speed.  —  Mr.  Alfred  Watkins 
in  a  recent  book,  "  Photography:  Its  Principles  and 
Applications,"  describes  a  new  method  of  finding  a 
value  which  he  calls  the  central  speed  of  a  plate.  It 
corresponds  to  the  middle  point  of  the  straight  line, 
and  of  it  Mr.  Watkins  says,  "  It  may  be  said  at  once 
that  this  central  speed  method  does  not  give  the 
maximum  speed  of  the  plate,  but  the  speed  which 
indicates  the  exposure  yielding  the  best  possible 
results,  and  if  the  same  emulsion  is  so  coated  on  two 
plates  as  to  give  a  thin  film  in  one  case  (short  period  of 
correct  exposure)  and  a  thick  film  in  another  case 
(long  period  of  correct  exposure),  the  poorer  film  will 
indicate  the  higher  speed.  This  is  best  when  the 
speed  is  used  for  purposes  of  practical  exposure,  but 
a  disadvantage  from  the  point  of  the  platemakers' 
competition  to  advertise  the  highest  speeds  for  their 
plates. 

"  The  writer  is  inclined  to  think  that  it  may  be 
advisable  to  make  two  speed  tests  of  a  plate:  the 
first,  made  by  an  observation  of  the  smallest  exposure 
which  gives  a  visible  deposit,  and  to  be  called  the 
maximum  speed  test,  being  right  for  snapshot  ex- 
posures and  advertising;  the  second,  made  by  the 
central  speed  plan,  being  right  for  time  exposures  for 
best  results." 

From  experience  with  Mr.  Watkins'  meter  and  the 


THE   SECRET   OF   EXPOSURE.  17 

list  of  plate  speeds  supplied  with  it,  we  are  inclined 
to  think  that  the  statements  of  Mr.  Driffield  and  of 
Mr.  Watkins  may  be  harmonized  as  follows:  Mr. 
Watkins  gives  numbers  which  we  think  represent  his 
"  central  speed."  The  average  user  believes  with  Mr. 
Driffield  and  finds  them  too  low,  hence  after  trial 
adopts  a  Watkins  plate  speed  number  much  higher 
than  the  one  on  the  card  and  probably  agreeing  pretty 
closely  with  Mr.  Watkins'  "  maximum  speed."  For 
example,  if  one  were  to  take  the  speed  of  an  average 
film  as  90,  as  printed  in  a  recent  speed  list,  and  give 
1-45  second  at/:8  with  a  light  value  of  2,  the  exposure 
would  probably  tend  to  produce  the  results  so  graph- 
ically described  above  by  Mr.  Driffield;  whereas 
a  speed  number  of  180,  indicating  an  exposure  of  1-90 
second,  would  undoubtedly  not  give  serious  under- 
time and  would  yield  a  quick-printing  negative  suitable 
for  most  modern  papers.  In  this  example  it  is  as- 
sumed that  the  shutter  speeds  are  accurate.  The 
same  result  is  reached  if  one  calculates  with  the 
printed  number,  90,  but  halves  the  indicated  exposure. 
The  Focal  Plane  meter,  however,  indicates  half  the 
Bee  exposure,  to  allow  for  snapshots  and  indicate  the 
shortest  possible  full  exposure.  The  same  correction 
holds  for  the  Wynne  Snap  Shot  meter.  In  the  same 
way,  other  films  listed  at  180  are  found  to  give  suffi- 
cient exposure  in  snapshot  work  if  the  speed  number 
350  be  used  in  calculating.  It  is  all  a  matter  of  actual 
trial  to  find  what  number  gives  the  results  desired  by 
the  individual.  In  fact,  Mr.  Watkins  says  in  his 
instructions,  under  "  Shutter  Photography,"  that  it 
"must  be  remembered  that  the  indication  is  {or full 
exposure  (the  one  giving  the  best  results),  and  that 


1 8  THE  SECRET  OF  EXPOSURE. 

half  this  is  as  much  as  is  generally  possible  to  give  under 
the  circumstances ;  indeed,  one-quarter  the  full  exposure 
often  passes  muster  as  '  good  for  a  snapshot.'  ' 

Variations  in  Plate  Speed.  —  Sometimes  one  batch 
of  plates  of  a  given  brand  will  test  twice  as  fast  as 
another  batch,  owing  to  variations  which  it  is  beyond 
human  skill  to  control.  Hence,  it  is  evident  that  no 
statement  of  the  speed  of  a  particular  sort  of  plate  can 
be  anything  but  an  approximation.  Notwithstanding 
this  drawback,  the  wise  buyer  who  sticks  to  one  kind 
seldom  finds  variation  enough  to  upset  his  calculations, 
because  so  many  other  sources  of  error,  such  as 
inaccurate  shutters,  enter  into  the  problem.  As  a 
general  thing,  plates  of  one  brand  will  not  depart  from 
their  average  speed  sufficiently  to  spoil  one's  results. 
In  some  factories,  the  finished  plates  are  tested  for 
speed  and  sorted  into  brands  according  to  the  readings 
obtained:  all  which  reach  the  top  speed  being  the 
high-priced  brand,  those  which  fall  short,  the  next 
cheaper,  and  so  on.  This  plan  is  to  the  advantage 
of  the  consumer,  as  far  as  uniformity  of  speed  goes. 

Variations  in  Shutter  Speeds.  —  Perhaps  the  most 
disturbing  variation  of  all  is  that  of  the  exposure 
shutter.  Few  between-the-lens  shutters  come  within 
a  reasonable  percentage  of  being  accurate.  A  speed 
marked  i-ioo  second  is  almost  never  faster  than  1-60 
and  sometimes  far  below  that.  The  more  expensive 
shutters  are,  however,  accurate  on  some  of  their 
speeds.  The  only  sure  way  to  control  results  is  to 
check  the  speeds  by  the  average  of  a  number  of  tests 
with  some  such  simple  device  as  the  Wynne  or  Picker- 
ing Shutter  Speed  Tester.  A  careful  worker  will  repeat 
the  tests  several  times  during  the  season,  as  tempera- 


THE  SECRET   OF   EXPOSURE.  19 

ture,  dust,  corrosion,  and  many  other  things  may 
seriously  alter  the  speeds.  Most  shutters  also  vary 
when  used  on  their  sides,  that  is,  when  the  kodak  is 
reversed  to  take  a  horizontal  picture.  The  slower 
speeds,  when  retarded  by  an  air  pump,  are  notoriously 
inaccurate  and  undependable.  The  subject  is  too 
large  to  go  into  in  detail,  but  the  reader  will  readily 
appreciate  that  to  know  what  he  is  doing  he  must  test 
his  own  shutter  and  know  how  fast  it  works.  As  a 
rule  it  is  quite  immaterial  what  the  speeds  really  are 
if  one  is  informed  of  the  actual  values  for  each  marking. 

Efficiency  of  Shutters.  —  Another  variation,  as 
between  shutters  of  different  models  or  types,  is  due 
to  the  higher  or  lower  efficiency  of  these  instruments. 
When  our  Tables  were  first  compiled,  practically  the 
only  shutters  were  of  a  two-blade  type  and  had  an 
efficiency  of  about  50  per  cent.  The  rather  full  times 
indicated  by  the  Tables  were  intended  to  allow  for 
this  low  efficiency,  hence  the  user  of  a  modern  sector 
shutter,  having  from  three  to  five  blades  and  an 
average  light-efficiency  of  about  85  per  cent,  will 
probably  find  it  possible  to  use  half  the  exposures 
indicated  by  the  Tables  and  still  get  good,  full  ex- 
posure. The  cheaper,  old-style  shutters,  on  the  other 
hand,  will  generally  need  the  full  Table  time. 

Focal-plane  shutters  are  generally  stated  to  be  100 
per  cent  efficient,  but  this  is,  of  course,  an  exaggera- 
tion. Careful  tests  made  abroad  proved  that  ten 
commercial  focal-plane  cameras  had  an  average 
efficiency  of  85  per  cent.  However,  many  users  do 
find  in  practical  work  with  their  reflecting  cameras 
that  they  can  give  exposures  as  fast  as  one-quarter  or 
one-sixth  those  called  for  by  our  Tables  and  still  get 


20  THE   SECRET  OF  EXPOSURE. 

satisfactory  results.  As  the  question  is  so  often 
asked,  we  would  suggest  that  each  user  of  a  focal-plane 
shutter  make  a  series  of  trial  exposures,  giving  half, 
one-quarter,  one-fifth,  and  one-sixth  the  times  of  the 
Tables  and  select  the  best-printing  negative.  All 
future  exposures  can  then  be  figured  by  the  Tables 
and  corrected  by  this  factor.  This,  naturally,  does 
not  apply  to  speed  photography,  but  only  to  deter- 
mining the  right  shutter  speed  to  employ  in  order  to 
secure  proper  rendering  of  the  shadows. 

More  about  Underexposure.  —  Consideration  of 
light  action  has  shown  us  that  there  is  a  minimum 
amount  of  light  needed  to  make  silver  bromide  de- 
velopable. If  the  exposure  is  regulated  so  that  not 
enough  particles  are  affected,  or  so  that  the  particles 
are  not  affected  enough  to  develop,  the  negative  lacks 
detail  throughout  and  shows  but  the  ghost  of  an 
image.  More,  but  still  insufficient,  exposure  may 
give  highlights  and  halftones  full  of  detail  (but  denser), 
and  blank  shadows.  A  slight  increase  may  give  much 
more  density  in  the  lights  and  hints  of  shadow  detail, 
the  whole  effect  being  extremely  contrasty.  Such  a 
negative  gives  a  "  soot  and  whitewash  "  print,  because 
the  dense  highlights  cannot  be  printed  through  before 
the  shadows  are  buried  in  blackness.  Finally,  we  may 
discriminate  against  a  plate  as  underexposed  if  any 
portion  of  the  shadow  detail  is  quite  bare  glass,  it 
being  presumed  that  all  objects  in  nature  reflect  some 
light  to  the  eye  and  also  affect  silver  bromide.  It  will 
teach  the  reader  more  about  exposure  to  expose  a 
series  of  plates  on  the  same  subject,  giving  times 
running  from  say  |  normal  to  normal,  and  de- 
veloping them  together  for  the  same  length  of  time 


THE  SECRET  OF  EXPOSURE.  21 

than  could  be  learned  in  any  other  way.  Exposure 
should  be  regulated  by  the  stop,  the  same  speed  of 
shutter  being  used  throughout.  The  gradual  building 
up  of  contrast  with  increasing  deposits  of  silver  in  the 
lights  and  the  attainment  of  maximum  useful  density 
are  thus  clearly  brought  out. 

More  About  Correct  Exposure.  —  Continuing  the 
series  of  exposures  recommended  in  the  last  para- 
graph, one  can  give  more  time  to  each  succeeding 
plate  and  note  the  latitude,  remembering  to  judge  by 
the  print,  as  pointed  out  by  Mr.  Driffield.  It  will 
generally  be  found  that  few  rapid  plates  will  stand 
more  than  six  or  eight  times  the  lower  normal  ex- 
posure without  rendering  the  gradations  of  tone 
wrongly;  in  other  words,  they  have  reached  the  limit 
of  their  latitude  and  are  overexposed.  The  experi- 
menter will  note  the  decrease  of  contrast  between 
highlights  and  shadows,  the  running  together  into  one 
uniform  grayness  of  the  highlights  and  the  halftones, 
and  the  clogging  up  of  the  shadows  with  superabun- 
dant detail. 

Latitude.  —  Latitude  varies  directly  as  the  quality 
of  the  plate.  Cheap  plates  are  invariably  poor  in 
silver,  and  though  they  may  seem  to  be  rather  rapid, 
they  have  so  thin  and  impoverished  a  film  that  they 
develop  through  to  the  back  very  quickly  and  yield 
only  a  weak  negative.  No  treatment  will  cause  them 
to  build  up  a  rich,  contrasty,  well-graded  negative. 
A  short  exposure  fails  to  impress  the  shadow  detail; 
a  correct  exposure  gives  somewhat  veiled  or  foggy 
shadows;  double  or  triple  the  shortest  normal  time 
produces  a  flat,  lifeless,  overtimed  result.  When  one 
pays  only  a  few  cents  a  dozen  more,  one  gets  better 


22  THE  SECRET   OF   EXPOSURE. 

glass,  and  a  thicker,  richer  film,  with  greatly  increased 
latitude  and  better  quality  throughout.  Other  things 
being  equal,  the  thicker  the  film,  the  greater  the 
latitude.  Double-coated  plates,  therefore,  which  have 
a  very  rich,  opaque,  slow  emulsion  next  to  the  glass 
and  a  rapid  one  coated  over  it,  possess  enough  latitude 
to  handle  the  most  difficult  kinds  of  subjects,  such  as 
interiors  with  sunlighted  landscapes  showing  through 
the  open  windows.  Ordinary  plates  and  films,  though 
quite  efficient  for  average  subjects,  are  not  capable  of 
handling  the  extreme  contrasts  presented  by  such 
subjects.  Hydra  plates  will  surpass  even  the  double- 
coated,  in  difficult  cases,  but  ordinary  plates  often 
cannot  be  exposed  correctly  for  all  the  tones,  and  a 
compromise  must  be  found  which  will  render  most 
of  the  values  accurately  enough  to  suggest  the  original 
in  a  well-made  print. 

Latitude  also  varies  considerably  with  speed.  The 
ultra-rapid  plates  of  our  Class  J,  equivalent  to  Wat- 
kins  500  or  Wynne  F  156,  are  designed  particularly 
for  extremely  short  exposures.  They  utilize,  in  fact, 
practically  only  the  underexposure  portion  of  the  H. 
and  D.  curve.  If  they  are  given  full  time,  the  results 
do  not  show  such  good  general  quality  as  can  be 
obtained  with  a  Class  I  or  a  Class  ij  plate.  The 
ultra-rapid  plates  are  generally  markedly  sensitive  to 
red,  hence  are  easily  fogged  by  common  ruby  dark- 
room light.  They  have  poor  keeping  qualities.  They 
tend  to  give  chemical  fog  or  surface  markings  and 
mottling  when  affected  by  age,  moisture,  or  heat. 
They  have  so  little  latitude  that  the  exposure  must  be 
determined  with  the  utmost  exactitude  or  the  results 
will  be  weak,  flat,  and  characterless.  Still,  in  their 


THE  SECRET  OF   EXPOSURE.  23 

particular  field,  when  only  the  most  rapid  plate 
possible  will  answer,  they  are  excellent. 

Modern  films  (and  their  equivalent,  the  double- 
coated,  orthochromatic  plate)  have  great  latitude, 
with  speed  enough  for  most  requirements,  and  will  be 
found  very  satisfactory. 

Correct  exposure,  then,  we  may  conclude,  is  that 
which  renders  the  relative  gradations  of  tone  as  they 
appear  to  the  eye  —  barring  orthochromatic  render- 
ing, which  is  "  another  story,"  as  Kipling  says. 
Incorrect  exposure,  as  we  have  seen,  gives  false  con- 
trasts, but  it  must  not  be  thought  that  it  is  the  function 
of  exposure  to  regulate  contrasts,  except  as  the 
pictorial  worker  aims  to  alter  them  for  liis  artistic 
purpose.  The  chief  concern  of  exposure  is  to  secure 
a  record  of  the  different  amounts  of  light  reflected  from 
the  objects  in  front  of  the  lens  —  to  give  a  true  render- 
ing of  the  relative  lightness  or  darkness  of  each  tone. 
Once  this  is  secured,  automatic  development  for 
exactly  the  time  found  right  by  experiment  will  give 
the  amount  of  contrast  seen  by  the  eye  (except  for 
non-orthochromatic  rendering).* 

It  is  apparent  that  nothing  which  can  be  done  to 
the  plate  in  the  darkroom  has  a  great  deal  of  effect 
upon  it  as  compared  to  the  exposure  which  went 
before.  The  fate  of  the  picture  has  been  sealed  when 
the  shutter  has  closed  and  the  kodaker  turns  the  key 
to  wind  on  a  fresh  section  of  film.  The  one  important 
problem  in  taking  every  picture  is  "  How  much  time 
shall  I  give?  "  Let  us  now  consider  means  to  solve 
this  problem. 

*  See  the  Thermo  Card,  sent  postpaid  for  25  cents  by  our 
publishers. 


THE  SECRET   OF   EXPOSURE. 


A  Practical  Guide  to  Correct  Exposure.  —  A  num- 
ber of  years  ago,  F.  Dundas  Todd,  editor  of  The 
Photo-Beacon,  drew  up  a  series  of  tables  based  on 
exhaustive  experiments  and  checked  by  repeated 
practical  tests  in  the  field.  His  idea  was  to  assign  to 
each  element  concerned  an  arbitrary  number,  to  add 
together  the  appropriate  numbers,  and  from  their  sum 
to  determine  the  necessary  exposure.  We  reproduce 
herewith  these  tables  in  their  latest  form,  and  the 
interested  reader  will  find  them  each  month  in  both 
American  Photography  and  Popular  Photography  with 
new  plates  listed  as  they  are  introduced,  and  changes  in 
speeds  made  as  needed.  They  may  also  be  had  from 
our  publishers  in  pocket  form,  with  an  exposure  record, 
for  25  cents,  postpaid. 

The  American  Photography  Exposure-Tables.*  — 
Find  numbers  for  subject,  stop,  light,  m6nth  and 
hour,  and  plate.  Add  them,  refer  to  table  (page  28), 
and  give  exposure  indicated.  When  the  exposure 
fails  to  correspond  with  speed  marking  on  shutter, 
use  the  nearest  shutter  speed,  preferably  the  lower. 

Subject.  - 

Sea  (only)  and  clouds \ 

Sea  views,  snow  scenes,  distant  landscape I 

Open  landscape  with  unimportant  foreground 2 

Average  landscape  with  foreground 3 

Landscape  with  dark  foreground,  groups  in  sunlight       4 

Street  scenes,  buildings,  groups 5 

Portraits  in  shade 7 

Indoor  portraits 8  to  10 

Interiors 8  to  16 

Stop. — 


/       2    1 

U.  S.  0.25  A 


o.33 


0-5 


£?  21  f  3  #3* 


6.7/1  1 

2.8^2 


/.8 
U.S.  4 


16  17 
16  ' 


£8 


9    4UO 


*  Copyright,  1906,  by  F.  Dundas  Todd.    Copyright,  1911,  1913, 
1914,  by  F.  R.  Fraprie. 


THE   SECRET   OF   EXPOSURE. 


Light.  - 

Intense  sunlight  (inky-black  shadows) o 

Bright  sunlight  (strong  shadows) £ 

Faint  shadow  cast  by  sun I 

Dull  (no  shadows) i  \ 

Very  dull  (whole  sky  very  dark) 2 

If  sunlight  falls  over  one  shoulder,  add  o;  if  straight 
across  subject,  add  I ;  if  sun  is  ahead,  add  2  (see  Fig. 
17).  When  using  back  combination  only  of  R.  R.  or 
symmetrical  lens,  add  2,  unless  actual  /  value  of  stop 
is  known  and  used. 

Month  and  Hour.  —  (For  latitude  40°  N.) 


A.    P. 
M.    M. 

June. 

May, 
July. 

Apr.,    ' 
Aug. 

Mar., 
Sept. 

Feb., 
Oct. 

Jan., 

Nov. 

Dec. 

12 

0 

O 

o 

1 

1 

I 

I 

II       I 

0 

o 

o 

\ 

^ 

I 

I 

10       2 

0 

o 

i 

i 

I 

I* 

ii 

9     3 

i 

1 

1 

I 

I 

2 

2 

8     4 

I 

I 

I 

2 

2 

3 

4 

7     S 

I 

I* 

3 

4 

5 

5 

5 

6     6 

2 

-2 

4 

c      7 

C 

Plate.  —  Nota  Bene.  —  The  numbers  indicate  ex- 
posure factors  for  use  with  our  Tables  and  the  letters 
development  speeds  for  Thermo  Development. 


A  merican  — 
Extra  Rapid 

-• 

Red  Seal  I 
Red  Diamond.    .    .  .      i  \ 

M 
MS 

A  nsco  — 

Self-screen  Ortho  ...     2 

CCQ                                                 1 

MS 

Film  and  Pack  
Speedex  Film 

I  2    -5 

i    VS 

Barnet  — 
Film  

Burke  and  James  — 
Atlas  Film  i\ 

S 

Superspeed  Ortho.  .  . 
Ortho  Extra  Rapid.  . 

i    M 
2    MS 

Central  — 
Special  XX.  .                   1 

VS 

26 


THE   SECRET   OF   EXPOSURE. 


Special    Home    Por- 
trait 

Extra     Fast     (Blue 
\  S                    Label) 

TJ 

M 

Special  

M           Aurora  Extra  Fast  .  . 

T^ 

MS 

Special  Non-halation 
Comet 

,  MS         Ortho  Extra  Fast  .-  .  . 
-  M           Ortho  Non-halation 

tj 
2 

M 
M 

Colornon 

MQ        Fast 

0 

MO 

Panortho  

MQ        Ortho  Slow  
Slow 

1 

VQ 

Cramer  — 
Crown  .    .        i 

S                Ilford  - 

Anchor      .                 .     2 

MQ        Monarch  

I 

VS 

Banner  X                        i  • 

L  S             Zenith  .  .  .  

J  1 

VS 

Instantaneous  Iso.  .      I 
Medium  Iso  2 
Commercial  Isonon.     2 

'->  MQ        Special  Rapid  
MQ         Chromatic  
MQ         Rapid  Chromatic..  . 
M           Ordinary   

2 

2 
1 

VS 

M 
O 

MQ        Process  

Q 

Slow  Iso  5 
Contrast                         9 

MQ            Imperial- 

Spectrum                        2 

MQ        Flashlight..      

I 

M 

Defender  — 
Vulcan  Film  i^ 
Vulcan  (Plate)  i 

Orthn                                         2 

Special  Sensitive  .  .  . 
Orthochrome  Special 
.  g                 Sensitive  
M           Special  Rapid  225  .  . 
MQ        Duonon  

1 

MQ 
MQ 

Non-halation  Ortho.     2 

MQ        Special  Rapid  200.  . 
WO       Non-filter  

2 
2 

S    ' 
MO 

Q^       Process  

9 

Dufay  — 
Dioptichrome  (with 
filter)                 .      7 

Jougla  — 
Violet  Label  
Green  Label  

2 

Eastman  — 
Motion-picture  Film 
Portrait  (flat)  Film.. 
Speed  Film  
Graflex  Film 

Omnicolore    (with 
filter)  

M|             Kodak  - 
VS          Speed  Film  
TTQ          Graflex  Film  

7 

i 

i 

VS 
VS 

Hawk-Eye  Film..  .  .        \ 

c             N.  C.  Film  
o             Kodoid  Plate 

yi 

s 

N    C    Film           .    .        -' 

2 

Ensign  — 
Film        i^ 

Hawk-Eye  Film.  .  .  . 
Motion-picture  Film 
-  MS         Portrait  (flat)  Film 

*i 

S 
MS 
MS 

Forbes  — 
Challenge  i^ 

Lumiere  — 
f  VQ         Sigma  

4 

s 

Q*         Blue  Label  

T  o 

MO 

Film  

T  i 

S 

Hammer  — 

Ortho  A  

2 

M 

Special    Extra    Fast 
(Red  Label)  ...      i 

Ortho  B  
MS         Panchro  C  

2 

2 

MQ 
MS 

THE   SECRET   OF   EXPOSURE. 


Autochrome      (Out- 

Color Value  i    M 

doors)  

7" 

\ 

Gilt  Edge  27  i|  MS 

Autochrome         (In- 

L Ortho  i£  MQ 

doors)  .  .  :  

8 

\ 

26  X  2  MS 

Slow  

9 

MQ 

Non-halation  2    MQ 

Marion  — 

Non-halation      L 

i 

g 

Ortho  2    MQ 

Brilliant  

PC 

I 

S 
MS 

Tropical  2    M 
C  Ortho  2\  VQ 

Panchromatic  2^  VQ 

New  Record  — 

23  3    MQ 

Extra  Fast  

2 

VS 

Process  9 

Paget  — 

Standard  — 

XXX  

2> 

M 

Fvtra                                      T  l  MO 

xxxxx  

Swift  
Extra  Special  Rapid 
Ortho  Extra  Special 
Rapid  

2 
I 
I 

T^ 

MS 

S 
S 

Imperial  Portrait.  ..      i^  MQ 
Orthonon  i£  MQ 
Polychrome  i|  MQ 
Thermic  i£  MQ 

Panchro  Ordinary  .  . 

2 

Q 

Stanley  — 

Panchro    Color    (no 

50  i\  M 

screen)  

2? 

VQ 

Commercial  4    MQ 

Special  Rapid  
Hydra  Panchro  .... 
Hydra  Rapid  

Premo  — 

l\ 

MQ 
MQ 

Wellington  — 
Extreme  \  S 
'Xtra  Speedy  i     MS 
Film  1  1  M 

Filmpack  

I] 

S 

Iso  Speedy  \\  M 

Speed  Pack  

I 

VS 

Portrait  Speedy  \\  M 

Roebuck  — 

Anti-screen  i  \  M 

Blue  Label  

T 

S 

Speedy  Special  Rapid    2     MS 

D.  C.  Ortho  

2 

MQ 

Ortho  Process  9    M 

Ortho  

.2 

MQ 

Wratten  &  Wainwright  — 

Rogers  — 

Panchromatic  i\  MQ 

Regular  

I 

S 

Process  3    Q 

Orthochromatic  .... 

2 

MQ 

Ortho  Non-halation. 

2 

MQ 

N.B.  —  Process    plates    are 

Seed  — 

usually  exposed  as  if  they  were 

Graflex  

i 

S 

Class  4^  to  Class  3  when  used 

Gilt  Edge  30  

MS 

for  copying  line  drawings. 

Plate  Speeds.  —  The  plate  factors  are  intended  to 
indicate  a  fair  average  value  for  each  brand  so  that 
users  will  be  sure  of  giving  proper  (full)  exposure  if 
they  follow  the  tables.  It  is  a  well-known  fact, 


28 


THE  SECRET  OF  EXPOSURE. 


however,  that  plates  vary  in  speed,  the  tendency  of 
most  brands  being  to  become  faster  as  years  pass. 
Two  boxes  of  the  same  brand,  sometimes  of  the  same 
batch,  will  occasionally  vary  50  per  cent  or  more  in 
speed. 

Exposure.  —  The  following  table  shows  the  exposure 
corresponding  to  the  number  found  by  adding  the  five 
factors. 


JU 


4i   ? 

2   1555 


94 


11  A 


14  f 


141 


16? 


161 


17 


181 


19 


20,1 


20i2s3 


22  « 


22i 


23 


23 


24  M 


25 


26* 


2M4 


273M0 


274  M 


45 


28? 


29 


30 


30 


THE   SECRET   OF   EXPOSURE.  29 

Caution!  —  Avoid  underexposure,  and,  in  case  of 
doubt,  give  more  than  the  Tables  indicate  rather  than 
less.  Underexposed  films  will  never  give  satisfactory 
prints,  but  any  reasonably  full  exposure  will  give  a 
good  print  if  fully  developed. 

An  Example.  —  Let  us  suppose  a  case.  You  are 
about  to  photograph  an 

Average  landscape 3 

Using  stop/: 1 1  (U.S.  No.  8) 6 

Light  is  intense o 

Time,  n  A.M.,  in  July o 

You  are  using  Eastman  N.  C.  film i£ 

The  figures 'given  are  those  to  be  found  in  the  Tables 
opposite  the  different  conditions.  Adding  them 
together  we  get  ioj  as  the  total,  and  on  referring  to 
the  last  table  under  10^  we  find  1-40  second,  which  is 
the  exposure  to  give. 

Referring  to  the  instructions  on  page  24,  the  reader 
will  observe  that  there  are  five  elements  or  factors 
necessary  to  consider  in  determining  exposure  by 
these  Tables.  They  are:  subject,  stop,  light,  month 
and  hour,  and  plate.  Let  us  consider  them  a  little 
more  in  detail. 

The  Influence  of  Subject.  —  The  Tables  separate 
all  possible  pictures  into  eight  groups  having  arbi- 
trary values  from  |  to  16;  that  is,  requiring  exposures 
from  the  most  rapid  snapshots  to  prolonged  time- 
exposures  indoors.  The  division  is  based  principally 
upon  the  amount  of  actinic  light  which  is  reflected 
from  the  subject. 

"  Sea  (only)  and  clouds  "  (Fig.  5)  is  the  group 
requiring  the  least  exposure,  on  account  of  the  great 
brightness  of  the  sky,  which  is  a  secondary  source  of 


THE   SECRET   OF   EXPOSURE. 


Fig.  5.  —  Sea  only  and  Clouds 


F.  R.  Fraprie 


light,  owing  to  refraction  of  the  sun's  rays  from  dust 
particles  or  water  vapor,  reflection  from  clouds,  and 
the  throwing  back  of  most  of  the  light  from  the  water, 
the  color  of  which  is  extremely  actinic  as  well ;  so  that 
overexposure  is  the  commonest  mistake  made  by  the 
beginner.  There  should  be  no  difficulty  in  telling 
whether  a  given  view  comes  in  this  group,  for  the  use 
of  the  word  "  only  "  rules  out  all  other  seascapes  which 
contain  objects  such  as  ships  within  100  ft.  Red  or 
yellow  sunrise  or  sunset  clouds  require  more  exposure 
unless  a  color-sensitive  plate  is  used.  Very  faint 
white  clouds  take  half,  and  very  dark  storm  clouds 
twice  the  exposure. 

"  Sea  views  (Fig.  6),  snow  scenes  or  distant  (pano- 
ramic) landscape,"  is  the  next  group.  The  factor  is  I, 
showing  that  this  class  requires  50  per  cent  more  time 
than  the  preceding  group.  Here  we  may  include  all 
seascapes  which  have  ships  or  yachts  near  enough  to 


THE   SECRET   OF   EXPOSURE.  31 


A .  Schnutenhaus 


Fig.  6.  — Marine  View 


Forman  Banna 


Fig.  7. —  Snow  Scene 


THE  SECRET  OF  EXPOSURE. 


Fig.  8.  — Distant  Landscape 


Maynard  J.  Ames 


be  of  importance  in  the  composition  —  say  within 
100  ft.  in  the  case  of  large  ships  or  50  ft.  in  the  case 
of  yachts  and  small  boats.  Views  on  open  beaches 
or  on  river  banks  open  to  the  sky  and  away  from  trees 
or  buildings,  open  snow  scenes  with  no  dark  objects 
(Fig.  7),  and  any  other  subjects  in  which  the  principal 
objects  are  100  ft.  or  more  away  from  the  lens,  with  a 
flat,  well-lighted  foreground,  may  be  classed  as  i. 

By  "  distant  landscape  "  (Fig.  8)  is  meant  one 
taken  from  an  elevation  and  including  nothing  in  the 
foreground ;  that  is,  the  actual  middle  distance  of  the 
view  is  the  foreground  of  the  picture.  Such  subjects 
are  usually  spoken  of  as  panoramas,  and  most  objects 
are  miles  distant  from  the  lens.  Most  telephoto  sub- 
jects come  in  this  group,  as  well  as  aeroplanes  in  flight. 

"  Open  landscapes  with  unimportant  foreground," 
factor  2  (Fig.  9)  is  the  next  group.  The  difference 
between  the  groups  having  factors  of  I  and  2  is  this: 
In  class  I  everything  is  at  least  50  ft.  or  more  from  the 
lens.  If  one  goes  close  enough  to  the  principal  object, 


THE   SECRET   OF   EXPOSURE.  33 


M.  D.  Miller 
Fig.  9. — Open  landscape,  Unimportant  Foreground 

say  25  ft.,  the  subject  would  become  2,  and  would  re- 
quire good  rendering  of  shadow  detail  by  an  increased 
exposure.  The  foreground,  however,  is  flat  and  has  no 
marked  shadows;  hence  it  hardly  counts  in  settling  the 
exposure.  The  moment  any  dark  objects  come  within 
25  ft.,  whether  they  are  human  or  animal  figures, 
small  trees  or  bushes,  or  shadows  cast  by  objects  out- 
side the  field  of  view,  we  should  have  to  pass  to  the 
next  class,  value  3.  It  is  the  important  objects  near 
the  lens  or  the  shadows  in  the  foreground  which  have 
to  be  noted  most  carefully.  This  group  includes  open 
landscapes,  streets,  fields;  light-colored  buildings  in 
landscape;  men  or  animals  in  the  middle  distance; 
athletic  sports  from  spectators'  benches ;  beach  scenes 
with  dark  or  near  foreground  objects;  ships  and 


34 


THE   SECRET   OF   EXPOSURE. 


Fig.  10.  —  Average  landscape 


M.  D.  Miller 


yachts  in  dock  or  close  to  the  camera;  average  snow 
scenes  with  tree-trunks  or  other  dark  objects  within 
25  feet. 

"  Average  landscape  with  foreground  "  (Figs.  2  and 
10),  value  3.  This  is  the  largest  class  of  subjects 
likely  to  be  taken  by  the  beginner.  The  deciding 
point  is  that  the  main  interest  and  the  principal  object 
of  the  picture  are  centered  in  the  foreground,  or  the 
color  of  the  latter  is  dark,  whether  owing  to  shadows 
cast  across  it  or  to  the  deep  tone  of  the  materials  of 
which  it  is  composed.  Most  of  the  vacation  snaps 
of  parties  attempted  by  the  kodaker  fall  within  this 
group,  the  subjects  being  posed  in  full  sunlight  15  ft. 
or  more  from  the  lens.  The  moment  one  goes  closer, 
say  to  8  ft.,  the  exposure  would  need  to  be  doubled. 
Many  street  scenes  of  an  open  nature  should  be 


THE  SECRET  OF  EXPOSURE.  35 


M.  D.  Miller 
Fig.  ii. — Landscape  with  Dark  Foreground 

classed  as  average  landscapes.  Class  here  all  land- 
scapes with  foliage,  figures,  or  buildings  of  average 
color;  average  street  scenes  in  wide  streets  or  open 
squares  (not  narrow  canyons  of  city  streets) ;  full- 
length  figures  or  groups  open  to  sky;  views  with  the 
principal  object  about  25  ft.  from  lens. 

"  Landscape  with  dark  foreground,"  factor  4  (Fig. 
n).  This  group  is  the  same  as  the  last,  except  that 
the  foreground  is  darker  in  color,  or  is  in  shadow,  or 
the  principal  object  is  dark  and  nearer  the  lens  than 
25  feet.  It  includes  most  city  street  scenes  with 
shaded  foreground.  It  is  always  a  good  plan  to  use 
this  value  in  place  of  3  if  the  foreground  is  in  shadow. 

"  Street  scenes,  buildings,  groups  "  (Figs,  i,  12,  13, 
14),  value  5.  A  typical  street  scene  is  one  where  there 
are  houses  on  both  sides  of  the  way,  and  the  light  is 


THE   SECRET   OF   EXPOSURE. 


Fig.  12.  —  Street  Scene 


D.  Miller 


confined  to  a  relatively  narrow  strip  of  sky.  Where 
the  buildings  are  higher  it  may  be  necessary  to  give 
even  more  time  than  denoted  by  the  number  5,  as 
in  the  canyons  formed  between  modern  skyscrapers. 
Buildings  come  in  this  group  only  when  they  are  near 
and  form  the  main  part  of  the  picture. 

A  group  is  generally  posed  about  12  or  15  feet  from 
the  lens  on  steps  in  the  full  shade  of  a  building  and  not 
open  to  much  sky  light.  Details  of  architecture,  such 
as  piazzas,  doorways,  etc.,  may  be  placed  here;  also 
full-length  figures  in  the  shade.  (Fig.  15.) 

"  Portraits  in  shade  "  (Fig.  16),  value  7.  A  por- 
trait is  a  subject  which  requires  a  considerable  ex- 
posure as  compared  to  a  landscape.  Take  as  an 
example  a  man  standing  in  the  shade  of  a  house.  If 
he  were  photographed  full  length  with  the  ordinary 


THE  SECRET   OF   EXPOSURE.  37 


Fig.  13.  — Building 


W.  L.  F.  Wastell 


Fig.  14. — Group 


M.  D.  Miller 


38  THE  SECRET  OF  EXPOSURE. 


Frau  Clara  von  Watjen 
Fig.  15.— Figure  in  Shade 

outfit,  he  would  count  as  5;  but  as  soon  as  one  goes 
close  enough  to  make  the  head  and  shoulders  fill  the 
picture  space,  the  exposure  must  be  greatly  increased. 
Single  meniscus  lenses,  working  at/:i6,  are  not  capable 
of  making  snapshots  of  such  subjects  without  appreci- 
able underexposure ;  but  a  bulb  exposure  will  generally 
yield  a  good  result,  say  about  J  second.  "  Portraits  " 
here  is  taken  to  mean  head-and-shoulder  pictures,  and 
half-length  studies.  In  this  class  belong  studies  of 
dark  foregrounds  very  close  to  the  lens,  or  fruit, 
flowers,  etc.,  in  shade  outdoors  and  only  5  or  6  feet 
from  the  lens. 


THE  SECRET  OF   EXPOSURE. 


39 


Wm.  R.  Read,  Jr. 
Fig.  16.  — Portrait  in  Shade  (Artificial  Background) 

Groups  consist  of  two  or  more  persons  at  such  a 
distance  from  the  camera  that  the  figures  nearly  fill 
the  picture  space.  If  the  same  persons  were  taken 
at  a  greater  distance,  the  subject  would  be  classed  as 
a  landscape.  Groups  are  usually  posed  in  the  shade, 
as  on  a  porch  open  to  the  sky,  or  under  trees,  and 
hence  require  a  long  exposure  owing  to  the  lessened 
illumination.  Groups  in  full  sunshine  may  be  taken 
with  a  large  stop  and  a  slow  snap.  They  often  fall 
in  Class  4. 

"  Indoor  portraits,"  value  8  to  10.  These  figures 
refer  to  home  portraits  taken  by  an  ordinary  window. 


40  THE   SECRET   OF   EXPOSURE. 

If  the  light  is  brilliant,  the  subject  near  the  window, 
the  surroundings  very  light  in  color  so  as  to  reflect  a 
great  deal  of  light,  a  white  reflector  used,  and  the 
sitter  dressed  in  white  or  light  colors,  the  value  8  would 
be  chosen.  A  dark  room,  small  window,  and  dark 
clothes  would  naturally  cause  one  to  calculate  with  a 
value  of  9  or  10.  Exposure  in  such  cases  is  a  matter 
of  seconds  and  will  vary  with  local  conditions,  hence 
the  value  of  this  class  may  be  changed  by  the  worker 
if  trial  exposures  make  an  alteration  seem  desirable. 

"  Interiors,"  value  8  to  16.  As  in  the  case  of  por- 
traits, the  individual  room  may  be  so  much  brighter 
than  the  one  represented  by  16  as  to  require  the  use 
of  a  different  number.  Here  again,  careful  tests  by 
actual  exposures  will  give  the  photographer  the  best 
idea  what  number  to  use  for  similar  conditions  of 
lighting  in  other  rooms.  Exposures  may  run  from  a 
few  seconds  to  several  hours  in  different  interiors,  such 
as  a  dainty  boudoir  or  a  gloomy  church.  The  general 
color  of  the  room  has  a  tremendous  influence.  Double- 
coated  ortho  plates  will  be  found  most  generally 
useful. 

The  reader  will  have  noted  that  in  this  system  of 
exposure  by  tables  the  accurate  placing  of  the  subject 
is  of  great  importance.  The  subjects  requiring  the 
least  exposures  are  those  of  highly  actinic  color  or  far 
distant  from  the  lens,  so  that  the  veil  of  luminous 
atmosphere  partly  obliterates  the  local  color  and 
introduces  rays  from  the  violet  end  of  the  spectrum. 
These  subjects,  it  may  also  be  noted,  have  relatively 
little  contrast  between  the  tones.  As  a  general  rule, 
all  objects  distant  more  than  24  times  the  focus  of  the 
lens  require  the  same  exposure.  For  a  6j-in.  lens  on 


THE  SECRET    OF    EXPOSURE.  41 

a  3  A  Kodak,  this  distance  is  13  ft.  Let  us  trace  the 
influence  of  distance  in  the  case  of  a  single  man.  At 
25  ft.  he  would  count  as  part  of  the  landscape  and  be 
called  average  landscape  with  foreground.  At  13  ft. 
he  would  fall  into  the  class  of  street  scenes,  buildings, 
groups;  at  6  or  7  ft.  portraits  in  shade  would  be  suit- 
able —  all  this  while  the  subject  stood  still  and  the 
camera  was  moved  towards  him. 

Part  of  the  difference  just  noted  is  due  to  the  effect 
of  distance  and  part  to  the  fact  that  objects  repro- 
duced on  a  large  scale  require  finer  rendering  of  detail, 
particularly  in  the  shadows,  to  satisfy  the  eye.  In 
painting,  for  instance,  one  might  represent  a  gray 
horse  in  the  middle  distance  by  a  single  brushful  of 
paint,  loosely  put  on  and  dragged  roughly  into  shape; 
but  if  one  were  representing  the  horse  in  the  fore- 
ground, it  would  have  to  be  carefully  and  minutely 
drawn  and  colored.  Contrast  increases  as  the  layer  of 
air  between  lens  and  object  diminishes.  The  greater 
the  contrast,  the  fuller  the  exposure  should  be.  "  Ex- 
pose for  the  shadows  and  develop  for  the  highlights." 

Orthochromatic  Effect.  —  To  some  extent,  the 
judgment  of  exposure  must  depend  on  the  sensitive- 
ness of  the  plate  to  different  colors.  Red,  orange, 
yellow,  yellow-green,  and  green  affect  plain  (non- 
orthochromatic)  plates  only  as  they  reflect  ultra-violet 
and  blue  light.  Blue-green,  the  color  of  most  summer 
foliage,  is  particularly  slow  to  impress  the  plate.  Thus 
most  photographs  record  the  relative  brightness  of  the 
objects  in  a  scene  quite  incorrectly,  being  sensitive 
chiefly  to  the  invisible  ultra-violet  and  the  visible 
violet  and  blue-violet.  These  facts  explain  why  it  is 
necessary  to  give  a  great  deal  of  exposure  to  get  the  de- 


42  THE  SECRET   OF   EXPOSURE. 

tail  in  dark-green  foliage  near  the  lens,  because  the 
amount  of  ultra-violet  reflected  diminishes  with  the 
nearness  of  the  object  and  the  local  color  itself  hardly 
affects  the  plate  at  all.  Orthochromatic  (or  isochro- 
matic)  films  and  plates  are  sensitive  to  the  yellow  and 
the  yellow-green,  but  almost  totally  insensitive  to 
blue-green,  and  hence  the  user  has  to  keep  in  mind  the 
color  of  the  foliage  and  modify  exposure  aqcordingly. 

Exposure  with  a  Rayfilter.  —  When  a  color-screen 
or  rayfilter  is  used,  the  exposure  must  be  increased  in 
proportion  to  the  depth  of  tint  of  the  filter.  Screens 
are  usually  sold  as  "  three- times,"  "  four- times,"  etc., 
the  maker  furnishing  the  proper  multiplying  factor. 
If  one  desires  to  get  the  best  possible  results,  it  is 
wisest  to  test  the  supposed  factor  by  actual  trial. 
Make  a  series  of  exposures,  giving  factors  both  higher 
and  lower  than  the  supposedly  correct  one  and  choose 
the  best-printing  negative.  A  given  filter  may  be  a 
2X  with  one  make  of  ortho  plate  and  a  4X  or  even 
6X  with  another.  In  this  connection,  it  is  well  to 
state  that  the  low-priced  yellow-brown-glass  screens 
are  not  worth  using.  Better  pay  a  fair  price  and  get 
a  spectroscopically  adjusted  screen,  preferably  one 
made  of  Filter  Yellow  K  and  requiring  about  2  to 
4  times  increase  of  exposure.  Old  filters  generally 
bleach  after  long  exposure  to  light  and  therefore  be- 
come quicker,  or  else  turn  brown  and  become  slower. 

The  Influence  of  Excessive  Contrast.  —  Some  sub- 
jects cannot  be  accurately  exposed  for  all  portions 
because  of  the  tremendous  difference  in  the  lumi- 
nosities of  the  different  parts.  Thus,  in  landscape, 
the  sky  is  overtimed  if  the  dark  foliage  in  the  fore- 
ground be  given  enough  time;  or  if  the  exposure  be 


THE  SECRET   OF   EXPOSURE.  43 

cut  to  save  the  clouds,  the  shadows  are  painfully 
blank.  It  is  all  a  case  of  compromise,  at  best;  and 
the  single-coated  plate  cannot  compete  with  the 
double-coated  in  handling  contrasts.  The  old  "  gold- 
en rule  of  photography"  must  be  borne  in  mind: 
"  Expose  for  the  shadows  and  let  the  highlights  take 
care  of  themselves."  Then,  if  one  "  develops  for  the 
highlights  and  lets  the  shadows  take  care  of  them- 
selves," the  rendering  will  be  as  good  as  the  particular 
brand  of  plate  can  give;  but  failure  is  sure  to  occur  if 
subjects  having  excessive  contrasts  are  attempted. 

Partial  Reversal.  —  When  a  plate  is  fully  timed, 
the  sky  becomes  somewhat  thinner,  owing  to  its  being 
overtimed  and  thereby  partly  reversed;  but  too  long 
an  exposure  will  yield  a  flat,  gray,  muddy  effect  as  the 
reversal  proceeds  too  far. 

The  Stops.  —  Two  methods  of  marking  the  aper- 
tures of  the  lens  are  in  common  use,  -the  /  or  focal 
fraction,  and  the  U.  S.,  or  Uniform  System,  numbers. 
The  /  system  is  based  on  the  diameters  of  the  open- 
ings. For  example,  a  lens  has  a  focus  of  8  in.  and  a 
stop  i  in.  in  diameter.  8  -r-  1=8,  and  the  stop  is 
marked  /:8.  A  stop  having  half  this  diameter,  or 
J  in.,  would  have  a  value  of  8  -f-  J,  or  16,  and  the 
stop  would  be/: 1 6.  The  relative  exposures  with  these 
openings,  however,  are  not  in  the  ratio  of  8  : 16  or  I  :  2. 
The  exposure  with  a  given  opening  depends  on  its  area. 
Now,  the  areas  of  circles  are  proportionate  to  the 
squares  of  their  diameters.  The  square  of  8  is  64 
(8X8  =  64)  and  the  square  of  16  is  256  (16  X  16  = 
256) ;  hence,  the  ratio  is  64  :  256,  or  1:4.  Hence 
/:i6  requires  four  times  the  exposure  needed  for  /:8. 
In  practice,  the  /  system  is  simplified  by  choosing 


44  THE   SECRET   OF   EXPOSURE. 

apertures  such  that  each  smaller  one  shall  have  half 
the  area  of  the  preceding  and  thus  require  double  the 
exposure.  The  series  usually  chosen  is: 

/:4    /:5.6    /:8    /:ii    /:i6    /:22    /:32    /:45    /:64 

The  Uniform  System  starts  with  /:4  as  a  basis  and 
calls  it  U.  S.  I.  Thus  the  corresponding  values  are: 

U.S.I     U.S.2     U.S.4    U.S.8    U.S.I6    U.S.32     U.S.64    U.S.I28 
U.S.  256 

The  supposed  advantage  is  that  the  stops  requiring 
doubled  exposures  are  also  numerically  double  the 
preceding  ones;  but  no  one  who  has  learned  the  / 
system  finds  the  slightest  difficulty  in  remembering 
the  relative  exposures.  Most  cameras  and  kodaks 
fitted  with  rapid  rectilinear  lenses  are  marked  with 
Uniform  System  numbers.  The  important  thing  is 
always  to  say  whether  an  /  or  a  U.  S.  number  is  in- 
tended in  stating  data  of  pictures.  It  would  be  a  gain 
in  scientific  accuracy  of  thought  and  speech  if  the 
U.  S.  numbers  were  abandoned  and  only  the/ numbers 
used  hereafter.  The  tendency  seems  this  way,  owing 
to  the  almost  universal  marking  of  anastigmat  lenses 
with  /  numbers. 

Other  /  Systems.  —  Several  foreign  manufacturers 
have  at  different  times  used  focal  fraction  stop  mark- 
ings based  on  some  other  stop  than  /:4  as  a  starting 
point,  so  that  such  odd  values  as/:i8  or/:i9  may  be 
found  on  their  lenses.  We  cannot  too  strongly  de- 
precate the  multiplication  of  systems  of  stop  marking. 
The  standard  English  /  system,  as  described,  is  ade- 
quate, and  it  should  displace  all  others. 

The  nearest  regular  /  number  given  in  our  list  of 
stops  will  in  most  cases  come  near  enough  to  any  odd 


THE   SECRET   OF   EXPOSURE.  45 

/  number,  as  a  difference  of  less  than  50  per  cent  in 
exposure  is  hardly  demonstrable. 

How  to  Find  /  Values.  —  Roughly,  the  /  number  of 
the  stop  may  be  found  by  measuring  its  diameter  and 
dividing  this  number  into  the  focus.  Precisely,  it 
may  be  ascertained  in  the  following  manner,  pre- 
scribed by  the  Royal  Photographic  Society :  The  lens 
is  focused  on  an  infinitely  distant  object,  the  ground 
glass  removed,  and  an  opaque  screen  pierced  with  a 
pinhole  in  the  axis  of  the  lens  is  substituted.  An 
illuminant  is  placed  close  to  the  pinhole  and  the  diam- 
eter of  the  beam  of  light  measured  where  it  leaves  the 
surface  of  the  front  lens.  This  diameter  is  the  measure 
of  the  effective  aperture. 

Finding  the  Focus.  —  The  equivalent  focal  length 
is  found  well  enough  for  practical  purposes  by  focusing 
on  infinity  and  measuring  from  the  diaphragm  to  the 
surface  of  the  plate  or  film.  Divide  this  measurement 
by  the  diameter  of  the  beam  of  light  and  the  answer 
is  the  /  number  of  the  stop.  A  more  precise  method 
is  to  focus  an  object  exactly  "  same  size  "  and  divide 
the  distance  from  ground  glass  to  object  by  4  to  get 
the  equivalent  focus.  This  is  not  practicable  with  a 
short-bellows  camera,  of  course. 

Grubb's  Method.  —  The  easiest  as  well  as  the  most 
accurate  way  to  determine  the  focal  length  of  a  lens 
is  that  originated  by  Grubb.  It  may  be  used  with  a 
film  camera  by  temporarily  fixing  a  ground  glass  with 
its  ground  surface  in  contact  with  the  aluminum  rollers 
over  which  the  film  is  drawn.  On  the  ground  glass 
draw  two  vertical  lines  about  I  in.  from  the  margin  at 
each  side.  Now  set  up  the  camera  on  a  large  table  in 
front  of  a  window  and  place  a  sheet  of  white  paper 


46 


THE   SECRET   OF   EXPOSURE. 
C 


Fig.  17.  — Finding  Focal  Length 

under  it.  Focus  on  a  chimney  or  church  spire  on  the 
horizon  and  make  the  image  fall  upon  one  of  the  pencil 
lines.  Now  draw  a  pencil  line  BE  upon  the  paper 
along  the  side  of  the  camera  and  then  turn  the  camera 
until  the  image  falls  upon  the  other  line,  when  a 
second  pencil  line  AD  is  drawn  as  before.  After  this, 
remove  the  camera  and  prolong  the  lines  until  they 
intersect,  making  an  angle  at  C.  Now  measure  the 
distance  between  the  pencil  lines  upon  the  ground 
glass  and  lay  off  this  exact  distance  DE  so  as  to  form 
the  triangle  DEC.  See  Fig.  17.  Find  the  exact 
center  F  of  this  base  line  and  draw  FC.  The  length 
of  FC  is  then  the  equivalent  focus  of  the  lens. 

In  the  case  of  cheap  cameras  fitted  with  single 
lenses  the  stops  of  which  are  not  numbered  or  are 
marked  with  arbitrary  numbers  from  I  (largest 
opening)  to  4,  the  /  values  are  found  by  measuring 
from  the  stop  to  the  film  and  dividing  this  number 
by  the  diameter  of  the  stop.  It  will  probably  be 


THE  SECRET   OF   EXPOSURE. 


47 


found  that  the  largest  stop  in  such  a  case  is  between 
/:I2  and/:i5.  Suppose  it  to  be  / 114.  How  may  one 
use  such  a  value  with  the  Tables?  Let  us  compare 
it  with/:ii.  Eleven  squared  (n  X  n)  equals  121. 
Fourteen  squared  (14  X  14)  equals  196.  These  num- 
bers are  to  each  other  (approximately)  as  I  :  1.5, 
hence /:I4  will  require  1.5  times  as  much  exposure  as 
/:ii.  In  other  words,  it  is  50  per  cent  slower.  Now, 
in  the  tables, /:n  and/:i6  are  represented  by  6  and  7, 
respectively,  hence  a  good  value  for/:i4  would  be  6|. 
A  value  within  50  per  cent  is  sufficiently  close  to  be 
cared  for  by  the  latitude  of  the  plate,  in  most  cases. 
Variation  of  /  Values.  —  When  the  lens  is  extended 
in  copying  or  enlarging,  the  actual  working  focus  of 
the  lens  is  increased  so  greatly  that  the  /  number  is 
altered.  Even  in  taking  near  objects,  say  at  6  ft.,  this 
diminution  of  the  effective  aperture  of  the  stop  has 
to  be  compensated  for,  as  we  pointed  out  in  the  exam- 
ple of  photographing  the  man  at  different  distances. 
Mr.  Alfred  Watkins  gives  the  following  table  which 
compensates  for  the  alteration  of  the/ value  of  the  stop: 


Lanternslide  making 

Thin  neg. 

Med.  neg. 

Dense  neg. 

Copying 

Black  and 
white 

Photo- 
graph 

Colored 
object 

T  C 

times  focus  from  lens 

i 

i 

I 

in 

IT 

52 

3s 

| 

I 

Ji 

2 

°r 

| 

ij 

2^ 

i\ 

4 

2 

f 

I 

2 

4 

(copying  equal  size) 

The  numbers  in  the  table  are  multipliers  of  the  calculated  exposure  and  not 
table  factors  to  be  added  in  determining  it. 


48 


THE   SECRET   OF   EXPOSURE. 


Example.  —  You  are  copying  a  photograph  and 
find  after  focusing  that  the  picture  is  3J  times  the 
focus  of  the  lens  distant  by  measuring  from  lens  to 
picture  and  dividing  the  distance  by  the  focus  of  the 
lens.  In  this  case  the  copying  factor  is  I  and  the 
exposure  is  given  as  calculated.  Suppose  you  wish 
a  larger  image  and  find,  after  focusing,  that  the  focus 
of  the  lens  is  contained  in  the  distance  from  picture 
to  lens  only  2\  times.  The  copying  factor  is  now  \\ 
and  the  time  given  must  be  50- per  cent  more  than  the 
first  negative  received. 

Mr.  Watkins  also  gives  a  similar  table  for  enlarging. 
The  numbers  of  diameters  of  enlargement  are  found 
by  dividing  the  length  of  one  side  of  the  enlarged 
image  by  the  length  of  the  same  side  of  the  original 
negative. 


Enlarging 
diameters. 

Thin  neg. 

Med.  neg. 

Dense  neg. 

Equal  size 

j 

2 

4 

if; 

l£ 

3 

6 

2 

2j 

4i 

9 

2* 

3 

6 

12 

3 

4 

8 

16 

4 

64 

12\ 

25 

5 

9 

18 

36 

Example.  —  It  is  found  that  a  thin  negative  re- 
quires 30  seconds  when  projected  equal  size.  How 
much  time  is  needed  to  make  a  four-diameter  enlarge- 
ment, all  other  factors  remaining  the  same?  Multiply 
30  by  the  enlarging  factor  of  6J  found  under  "  thin 
negative  "  and  opposite  4  diameters.  The  answer  is 
1 88  seconds,  or  3  minutes,  8  seconds. 


THE  SECRET   OF   EXPOSURE.  49 

Other  Systems  of  Stop  Markings.  —  Some  lens- 
makers  mark  their  stops  with  variations  from  the 
standard  English  /  system  tabulated  above,  but  the 
user  can  readily  compare  the  values  by  squaring.  In 
the  same  way,  stops  of  fast  lenses,  such  as  /:3-8,  4.8, 
5.5,  6,  6.3,  6.5,  6.8,  7,  7.7,  etc.,  may  be  compared  with 
the  nearest  regular  /  number  and  the  percentage  of 
increased  speed  noted.  It  may  as  well  be  said,  how- 
ever, that  no  shutter  is  accurate  enough  to  make  much 
difference  as  between  /:7-7  and  /:8,  for  instance.  In 
the  same  way,  /:6.8  is  practically  equivalent  to  f:f. 
If  we  consider  /:8  as  requiring  an  exposure  of  unity, 
the  following  fractions  may  prove  useful  in  calculating 
the  minimum  exposure  allowable  for  snapshots  :/:8  = 
Jl  /:7  =  f  J  /;6-3  =  f-  For  instance,  if  we  have  deter- 
mined that  1—25  second  is  needed  at  /:8,  at  /:6.3  we 
could  give  5-8  of  1-25,  or  1-40  second,  probably  the 
marked  1-50  of  our  shutter.  Another  example:  a 
portrait  indoors  might  require  8  seconds  at  /:8,  but 
at/:6.3,  5  seconds  would  suffice. 

Speeds  of  Air-Space  and  Cemented  Lenses.  — 
Occasionally  confusion  arises  from  the  conflicting 
claims  of  lensmakers,  some  stating  that  air-space 
lenses  lose  light  by  reflection  and  are  slower  than  their 
nominal  /  numbers  would  indicate;  while  makers  of 
air-space  objectives,  per  contra,  assert  that  a  similar 
loss  is  due  to  absorption  by  the  thick  glasses  used  by 
their  rivals.  Both  are  right,  within  limits;  but  the 
loss  of  light,  in  the  most  unfavorable  cases,  can  hardly 
amount  to  25  per  cent,  and  this  variation  from  a 
calculated  exposure  is  negligible.  Besides,  the  maker 
ordinarily  allows  for  any  small  variations  in  marking 
his  stops,  so  that  the  values  found  on  any  good  lens 


50  THE  SECRET   OF   EXPOSURE. 

and  shutter  may  always  be  assumed  to  be  accurate  for 
practical  purposes.  All  lenses  marked,  for  instance, 
/:6.3,  may  be  taken  as  having  the  same  speed. 

Exposure  with  a  Single  Combination.  —  Most  R.  R. 
lenses  are  symmetrical,  that  is,  they  are  made  up  of 
two  "  landscape  "  or  "  single  view  "  lenses  each  of  a 
focal  length  approximately  double  that  of  the  com- 
bination. The  actual  diameter  of  the  stop  opening 
remains  the  same  whether  the  combinations  are  used 
together  or  separately,  but  its  /  value  varies.  Thus, 
if  the  diameter  is  I  in.  and  the  focus  of  the  doublet 
(both  combinations  in  place  in  the  shutter)  is  8  ins., 
the/ value  is/:8;  but  if  the  front  lens  is  removed  and 
the  same  stop  of  I  in.  is  used  with  the  rear  lens 
of  16  inches'  focus,  its  value  becomes  /:i6.  This  is 
why  the  Tables  direct,  "  When  using  rear  combina- 
tion of  lens  only,  add  2."  One  can,  of  course,  find  the 
real  /  value  of  any  stop  by  actual  measurement,  and 
then  no  addition  is  needed.  Some  makers  furnish  a 
shutter  for  "  convertible  "  lenses  with  the  stop  values 
for  the  doublet  and  each  of  the  single  combinations 
marked  on  the  scale.  In  other  cases,  doublets  are 
made  up  of  single  combinations  of  dissimilar  foci  and 
the  user  is  left  to  find  for  himself  the  proper  ratios  for 
his  stop  openings.  Here  it  is  best  to  make  a  scale  for 
one's  self  by  measuring  the  focal  length  of  each  com- 
bination from  diaphragm  to  plate  when  focusing  on  'a 
distant  object  and  dividing  the  diameters  for  each 
marking,  measured  on  a  wedge-shaped  strip  of  card, 
into  the  focus.  The  marked  /:8,  etc.,  can  then  be 
noted  down  as  being  really /:ii,  let  us  say,  for  the 
rear  combination  and  really  /:i8,  let  us  say,  for  the 
front  combination,  or  whatever  the  figures  may  be. 


THE   SECRET   OF   EXPOSURE.  51 

Light.  —  The  Tables  recognize  five  variations  in 
daylight  from  intense  sunlight  to  very  dull,  each 
decrease  in  intensity  representing  a  falling  off  of  50 
per  cent  in  actinic  value  of  the  light.  Smaller  per- 
centages would  have  no  measurable  effect.  "  In- 
tense sunlight  "  is  characterized  by  crisp,  dark 
shadows.  "  Bright  "  is  midway  between  intense  sun- 
light and  "  faint  shadow  cast  by  sun,"  and  may  be 
called  cloudy-bright,  intense  sunlight  generally  imply- 
ing few  or  no  clouds  in  the  sky.  It  is  easy  to  judge 
these  conditions  by  observing  the  shadows.  "  Dull  " 
is  the  condition  seen  when  the  sun  is  quite  obscured 
and  objects  cast  no  shadows.  "  Very  dull  "  is  a  value 
met  only  when  the  sky  is  wholly  covered  with  dark- 
colored  clouds. 

Month  and  Hour.  —  The  actinic  value  of  the  light 
changes  not  only  with  the  amount  of  water  vapor 
present  in  the  atmosphere,  but  also  with  the  altitude 
of  the  sun,  and  this  factor  is  cared  for  by  the  month 
and  hour  number.  Inasmuch  as  the  summer  sol- 
stice occurs  in  June,  the  four  summer  months,  from  the 
middle  of  April  through  the  middle  of  August,  have 
about  the  same  mean  altitude  of  the  sun  and  the  values 
are  about  the  same  at  the  same  hours.  The  Tables  are 
most  reliable  during  the  middle  hours  of  the  day,  for 
yellow  or  reddish  light  early  or  late  in  the  day  is 
almost  impossible  to  gauge  by  the  eye.  When  the 
sun  is  sinking  rapidly,  exposure  changes  very  quickly 
in  a  few  minutes,  particularly  if  plain  plates  are  used. 
With  the  modern  orthochromatic  films,  the  numbers 
will  be  found  reasonably  correct,  but  the  operator 
cannot  dispense  with  judgment  and  must  rely  on  past 


THE  SECRET   OF   EXPOSURE. 


experiences  for  exposures  made  before  7  A.M.  and 
after  5  P.M. 

Altitude.  —  Generally  speaking,  no  shortening  of 
exposure  need  be  made  for  altitude  above  sea  level, 
unless  it  exceeds  5000  feet,  when  three-quarters  of  the 
calculated  exposure  may  be  given.  Over  10,000  ft., 
half  the  regular  time  would  be  sufficient. 

Latitude.  —  The  table  already  given  is  intended  for 
use  in  the  northern  part  of  the  United  States,  about  35 
to  45  degrees  north  latitude.  This  belt  includes  New- 
berne,  N.  C.,  to  Bangor,  Memphis  to  St.  Paul,  and 
Santa  F6  and  Los  Angeles  to  Salem,  Ore.  The  fol- 
lowing tables  cover  the  settled  portions  of  the  world 
at  intervals  of  about  10  degrees  of  latitude.  The 
months  for  latitudes  north  of  the  equator  are  given 
at  the  top  of  the  tables,  while  those  for  the  southern 
hemisphere  are  below. 

For  60°  N.  Southern  Siberia,  Southern  Alaska,  Northern  Canada, 
Iceland,  Norway,  Sweden,  and  Northern  Russia. 


A.    P. 

M.    M. 

June. 

May, 
July. 

Apr., 
Aug. 

Mar., 
Sept. 

Feb., 
Oct. 

Jan., 
Nov. 

Dec. 

12 
II       I 
10       2 

9-3 

O 
O 

O 

1 

I 

1 

I 
I 

ii 

I 
ij 
ll 

2 

ii 

2 
2 
? 

2 
3 
4 
e 

3 

6 

8     4 
7^ 

I 
zl 

ll 

2 

2 

•3 

3 

e 

5 

6    6 

2 

e 

i?       7 

•y 

5' 

A     8 

Dec. 

Nov., 
Jan. 

Oct., 
Feb. 

Sept., 
Mar. 

Aug., 
Apr. 

My, 

May. 

June. 

THE  SECRET   OF   EXPOSURE. 


53 


For  53°  N.    British  Isles,  Northern  Germany,  Southern  Canada, 
Southern  Russia. 


A.    P. 
M.    M. 

June. 

May, 
July. 

Apr, 
Aug. 

Mar, 
Sept. 

Feb., 
Oct. 

Jan., 

Nov. 

Dec. 

12 

O 

0 

1 

I 

I* 

2 

3 

II       I 

O 

O 

\ 

I 

2 

3 

4 

IO       2 

O 

O 

\ 

l^ 

2I 

4 

5 

9     3 

\ 

i 

I 

2 

3 

5 

7 

8     4 

I 

I 

I  7^ 

oi 

5 

7     5 

2 

2? 

c 

6     6 

2 

3 

5 

5     7 

5 

5 

4     8 

6 

Dec. 

Nov., 

Jan. 

Oct., 
Feb. 

Sept, 
Mar. 

Aug., 
Apr. 

May. 

June. 

For  40°  N.     Northern    United  States,   Armenia,   Spain,   Italy, 
Turkey,  Japan,  Greece,  Pekin,  and  Central  China. 


A.     P. 
M.    M. 

June. 

May, 
July. 

Apr, 
Aug. 

Mar, 
Sept. 

Feb., 
Oct. 

Jan, 
Nov. 

Dec. 

12 

O 

O 

O 

i 

1 

I 

I 

II       I 

0 

O 

O 

\ 

i 

I 

I 

10       2 

O 

0 

i 

i 

I 

jl 

jl 

9     3 

8     4 

i 

I 

i 

I 

I 
2 

I 

2 

2 

3 

2 

4 

7     5 
6     6 

2 

3 

3 

4 

4 

5 

5 

5 

c      7 

C 

Dec. 

Nov., 
Jan. 

Oct., 
Feb. 

Sept, 
Mar. 

Aug., 
Apr. 

July, 
May. 

June. 

40°  S.     New  South  Wales,  New  Zealand,  Argentina. 


54 


THE  SECRET   OF   EXPOSURE. 


For  30°  N.    Southern  China,  Southern  United  States,  Northern 
Mexico,  Northern  Africa,  Arabia,  Persia,  Northern  India. 


A.    P. 
M.    M. 

June. 

May, 
July. 

Apr., 
Aug. 

Mar., 
Sept. 

Feb., 
Oct. 

Jan., 
Nov. 

Dec. 

12 

-i 

O 

O 

O 

O 

i 

I 

II       I 

o 

o 

o 

o 

o 

I 

I 

10       2 

o 

o 

o 

o 

i 

I 

I 

9     3 

o 

o 

1 

i 

I 

I* 

2 

8     4 

i 

I 

l£ 

Ij 

2 

3 

7     ^ 

J  i 

2 

2~ 

c 

6     6 

6 

Dec. 

Nov., 
Jan. 

Oct., 

Feb. 

Sept., 
Mar. 

Aug., 
Apr. 

July, 

May. 

June. 

For  30°  5.    Southern  Australia,  Northern  Argentina,  Cape  Colony, 
Uruguay. 


For  23°  N.    India,  Mexico,  Southern  Egypt,  Central  Arabia, 
Cuba,  and  Northern  West  Indies. 


A.     P. 

M.    M. 

June. 

May, 
July. 

Apr., 
Aug. 

Mar., 
Sept. 

Feb., 
Oct. 

Jan., 
Nov. 

Dec. 

12 

i 

'\ 

£ 

O 

0 

O 

f 

II       I 

o 

o 

O 

O 

0 

\ 

I 

10       2 

0 

o 

o 

O 

i 

\ 

I 

9     3 

\ 

\ 

\ 

I 

i 

I 

i£ 

8     4 

I 

I 

I 

l£ 

12 

2 

2^ 

7     5 

2 

2 

2^ 

3 

z\ 

4 

7 

6     6 

6 

Dec. 

Nov., 
Jan. 

Oct., 

Feb. 

Sept., 

Mar. 

Aug., 
Apr. 

July, 
May. 

June. 

For  23°  5.   Northern  Australia,  Northern  Chile,  Bolivia,  Mada- 
gascar, Rio  Janeiro,  Transvaal. 


THE   SECRET   OF   EXPOSURE. 


55 


Tropics,  20°  N.  to  20°  5.     Northern  Brazil,  Canal  Zone,  Central 
Africa,  Ceylon,  Borneo,  Sumatra,  Pacific  Islands. 


A.    P. 
M.    M. 

June. 

May, 
July. 

Apr., 
Aug. 

Mar., 
Sept. 

Feb., 
Oct. 

Jan., 
Nov. 

Dec. 

12 

O 

O 

~\ 

-1 

-i 

0 

O 

II        I 

0 

O 

O 

O 

0 

O 

0 

IO       2 

O 

0 

0 

0 

O 

O 

O 

9     3 

I 

i 

i 

i 

1 

i 

I 

8     4 

ri 

I 

i 

I 

I 

i 

ii 

7     5' 

3 

3 

2| 

2* 

2^ 

3 

3 

Exposure  by  Length  of  Shadow.  —  A  very  ingenious 
method  of  determining  exposure  at  any  time  when  the 
sun  is  shining,  irrespective  of  latitude,  season,  or  time 
of  day,  is  given  by  Gaston  M.  Alves  in  Photo  Minia- 
ture, No.  54.  This  is  by  stepping  one's  own  shadow. 
"  A  person  usually  steps  in  regular,  natural  step, 
about  40  per  cent  of  his  own  height,  and  it  is  easy  to 
compute  mathematically  the  length  of  his  shadow  on 
level  ground,  at  given  altitudes  of  the  sun.  On 
reasonably  level  ground  let  the  operator  note  the  point 
where  his  shadow  reaches.  Then  let  him  measure 
the  distance  to  this  point  in  his  usual  steps."  The 
table  below  gives  numbers  which  combine  the  factors 
for  sunlight,  hour,  month,  latitude,  and  longitude,  and 
it  is  necessary  only  to  add  the  proper  numbers  for  the 
plate  and  stop  used,  to  determine  the  number  corre- 
sponding to  the  exposure  by  our  system: 

23  steps     1 5  steps     n  steps     7  steps     5  steps    3  steps     insteps 
6  52  5  4l  4  3?  3 

Direction  of  the  Lighting.  —  Ordinary  photographic 
lighting  outdoors  is  when  the  light  comes  from  over 
the  operator's  shoulder,  and  the  calculated  exposures 


THE   SECRET   OF   EXPOSURE. 


Harold  D.  Lafayette 
Fig.  18.  —  Exposure  with  Sun  Ahead 

will  be  found  correct  in  most  instances.  Once  in 
a  while,  however,  one  wishes  a  different  effect  and 
takes  the  picture  more  or  less  against  the  light. 
Here  the  shadows  at  once  occupy  a  larger  portion  of 
the  picture  and  accordingly  require  much  better 
rendering.  When  the  light  is  across  the  subject,  that 
is,  at  right  angles  to  the  axis  of  the  lens,  an  increase 
of  100  per  cent,  signified  by  adding  I,  is  needed  to 
prevent  the  shadows  from  coming  out  unnaturally 
black  and  lacking  in  detail.  Similarly,  when  the  sun 
is  on  the  axis  of  the  lens,  or  directly  ahead  (the  lens 
of  course  being  shielded  with  the  hat  or  the  plateholder 
slide  from  its  direct  rays),  the  exposure  has  to  be 
quadrupled,  as  indicated  by  the  instruction  to  add  2. 
See  Fig.  18. 


THE  SECRET   OF   EXPOSURE.  57 

Adjusting  Exposure  by  Trial.  —  No  system  of 
exposure  determination  can  be  exactly  fitted  to  the 
ideas  of  the  user  without  a  trial,  owing  to  inaccuracy 
of  shutter  speeds  and  to  some  extent  to  the  individ- 
ual's notion  of  a  perfectly-timed  negative  for  the 
printing  process  in  use.  Generous  rather  than  scant 
time,  however,  is  always  to  be  preferred,  for  a  well- 
timed  plate  can  always  be  made  to  yield  a  printable 
negative  by  judicious  development.  If  the  true 
gradation  of  the  tones  is  registered  on  the  sensitive 
film  by  adequate  exposure,  the  contrast  between  the 
tones  can  be  regulated  by  shorter  or  longer  develop- 
ment. Thus,  negatives  intended  for  bromide  enlarg- 
ing or  printing  on  gaslight  papers  must  not  be  carried 
so  far  as  those  intended  for  P.O. P.  or  carbon.  The 
ideally  perfect  negative  is  the  one  which  will  pro- 
duce the  kind  of  print  wanted  on  the  paper  in  use. 
It  is  therefore  advisable  for  the  user  of  these 
Tables  to  make  a  few  test  exposures  in  the  following 
manner. 

Select  a  landscape  subject  which  seems  to  you 
exactly  to  fill  the  definition  of  average  landscape  with 
foreground;  for  example,  a  view  with  trees  about 
25  ft.  from  the  lens  and  nothing  but  grass,  with  per- 
haps a  path  running  towards  the  trees,  nearer  than 
that  distance.  See  that  the  sun  is  shining  over  one 
shoulder,  illuminating  the  subject  so  as  to  cast  good 
shadows  in  the  foliage,  but  none  over  the  immediate 
foreground.  Calculate  the  exposure  with  the  values 
printed  in  the  Tables  for  the  particular  film  in 
use.  Let  us  take  the  example  already  given; 
namely, 


58  THE   SECRET   OF   EXPOSURE. 

Average  landscape 3 

Stop/: 1 1  (U.S.  No.  8) 6 

Intense  sunlight o 

1 1  A.M.  in  July o 

Eastman  Non-curling  film ji 

The  sum  is  roj  and  the  correct  exposure  is  1-40  second. 
The  test  may  be  made  so  as  to  check  the  speed  of  the 
shutter  and  the  speed  of  the  plate  at  the  same  time. 
Give  exposures  of  i-ioo,  1-50,  and  1-25  at  U.  S.  8. 
Develop  in  the  strip,  by  either  the  tank  or  the  tray 
method,  for  the  standard  time.  It  will  probably  be 
found  that  the  i-ioo  is  very  slightly  undertimed,  the 
1-50  about  right  and  the  1-25  slightly  full-timed.  In 
this  case,  you  could  reasonably  estimate  the  i-ioo  as 
1-60,  the  1-50  as  1-40,  and  the  1-25  as  1-25.  A 
shutter  which  gave  an  accurate  i-ioo  might  demon- 
strate decided  lack  of  detail  in  the  deepest  shadows, 
and  an  accurate  1-50  would  be  almost  correct.  Some- 
times the  1-25  is  extremely  slow,  not  more  than  1-12 
or  i-io,  and  in  this  case  the  exposure  made  at  this 
speed  would  be  considerably  more  than  necessary. 
Occasionally  there  is  no  appreciable  difference  be- 
tween 1-25,  1-50,  and  i-ioo. 

With  a  single-speed  shutter,  one  marked  simply 
"  I  "  for  the  snapshot,  the  speed  is  almost  sure  to  be 
between  1-20  and  1-40,  and  may  for  all  practical 
purposes  be  called  1-25.  If  such  a  shutter  is  fitted 
with  a  rapid  rectilinear  lens  working  up  to  U.  S.  4, 
the  trial  may  be  made  by  using  for  successive  exposures 
stops  U.  S.  4,  8,  and  16,  and  choosing  the  best-printing 
negative.  If  a  single  meniscus  achromatic  lens  is 
fitted,  the/ value  of  the  largest  stop  must  be  found  by 
measurement  as  previously  directed.  Suppose  it  to 


THE   SECRET   OF   EXPOSURE.  59 

be /:I4,  value  6J,  our  sum  then  becomes  II,  which 
indicates  an  exposure  of  1-25,  exactly  the  supposed 
speed  of  the  shutter.  If  the  film  is  undertimed,  it 
may  be  that  the  shutter  works  quicker  than  1-25;  if 
overtimed,  slower.  In  the  second  case  it  may  be 
possible  to  use  the  next  smaller  stop  without  getting 
serious  underexposure. 

The  user  of  the  cheaper  cameras  with  stops  num- 
bered from  i  to  4  can  employ  the  Tables  to  determine 
whether  the  only  snapshot  he  can  give  will  prove 
successful.  If  the  exposure  indicated  is  1—20  to  1—50, 
the  regular  snap  with  the  largest  stop  will  probably 
answer;  if  1-75  to  1-150,  the  second  (smaller)  stop 
can  be  used;  if  less  than  1-12,  hopeless  underexposure 
is  certain,  and  the  camera  must  be  used  on  a  tripod  for 
bulb  or  time  exposure.  If  the/  values  of  the  smaller 
stops  are  known,  the  exposures  may  be  calculated  in 
the  regular  manner,  using  the  correct  values  for  the 
actual  stops. 

On  the  other  hand,  if  the  speed  of  the  shutter  has 
been  tested  and  found  accurate  as  marked,  slight 
overexposure  may  occur.  In  this  case  it  may  be 
possible  to  alter  the  speed  number  of  the  film,  calling 
it  I  instead  of  ij;  or,  if  undertime  occurs  with  a 
tested  speed,  it  may  be  advisable  to  use  2  instead  of 
ij.  These  points  must  be  worked  out  by  the  in- 
dividual to  suit  his  own  ideas. 

Short  "Bulb"  and  "Time"  Exposures.  —  The 
beginner  equipped  with  a  single-lens  hand  camera, 
with  only  one  speed  of  snap,  will  realize  from  what 
has  been  said  that  his  chances  of  successful  pictures 
depend  almost  wholly  on  giving  enough  exposure. 
Outside  of  the  limits  worked  out  above,  he  will 


60  THE  SECRET   OF   EXPOSURE. 

therefore  fix  the  camera  to  a  tripod  and  use  smaller 
stops  with  "  bulb  "  or  "  time  "  exposure.  A  few  hints 
about  speeds  may  be  useful.  1-5  second  is  usually 
the  quickest  exposure  obtainable  by  setting  the 
shutter  to  "  bulb  "  and  pressing  and  releasing  the 
rubber  bulb  as  quickly  as  possible.  1-2  and  I  second 
are  similarly  obtained,  counting  "one  "  and  "  one-and- 
one  "  respectively.  A  little  practice  with  the  empty 
camera  soon  teaches  the  knack.  There  are  many 
schemes  of  counting  seconds.  One  of  the  best  is  to 
count,  "  one  thous-and,  two  thous-and,"  etc.,  saying 
three  syllables  slowly  in  time  with  a  watch.  A  half- 
second  pendulum  is  very  convenient.  This  is  made  by 
tying  a  small,  heavy  weight,  such  as  a  bullet  painted 
white,  to  a  string  just  short  of  10  ins.  long  —  that  is, 
the  complete  pendulum  is  between  9^  and  10  ins.  long. 
Seconds  are  counted  at  one  end  of  the  swing  only. 
Cameras  having  no  "  bulb  "  setting  may  be  operated 
on  the  "  time  "  setting  in  about  1-4  or  1-3  second  by 
opening  and  closing  the  shutter  as  quickly  as 
possible. 

One-tenth  second  is  about  the  slowest  exposure 
which  will  show  no  movement  when  the  camera  is 
held  in  the  hand.  Some  gifted  individuals  assert  that 
they  can  give  1—5,  1—2,  or  even  I  second  without  blur, 
but  the  writer  believes  their  shutters  work  much 
faster  than  supposed.  The  ideal  shutter  for  hand- 
camera  work  would  be  one  having  actual  speeds  of 
i-io,  I— 20,  and  1—40,  as  these  are  the  most  generally 
useful.  The  single-speed  shutter  is  by  no  means  to 
be  despised,  because  that  one  snap  is  a  reasonably 
constant  factor  and  exposure  is  accurately  regulated 
by  changing  the  stop. 


THE  SECRET   OF   EXPOSURE.  61 

Exposures  by  Artificial  Light.  —  The  modern  red- 
sensitive  ultra-rapid  plates  of  class  \  are  particularly 
suitable  for  making  exposures  by  firelight,  lamplight, 
and  the  various  forms  of  incandescent  lights,  including 
the  regular  Mazda  and  the  nitrogen-filled  bulbs. 
The  Cooper-Hewitt  light  is  very  fast  for  ordinary 
(blue-sensitive)  plates.  Many  of  the  orthochromatic 
plates  are  very  fast  to  Mazda  light.  In  general,  if 
two  plates  in  daylight  are  J  and  I,  their  speeds  will  be 
reversed  in  artificial  light,  unless  the  particular  light 
used  is  very  rich  in  red  rays.  Yellow  light  is  not  very 
actinic  to  the  class  \  plates,  slowing  them  to  class  I. 
It  raises  the  speed  of  an  ortho  plate  50  per  cent. 

It  is  hard  to  suggest  exposures  for  trial,  owing  to  the 
tremendous  variations  in  working  conditions.  With 
an/:4-5  lens,  a  color-sensitive  plate,  a  250- watt  Mazda, 
and  proper  reflectors,  however,  a  portrait  can  be  made 
in  a  few  seconds  at  most.  It  is  helpful  to  remember 
that  the  actinic  strength  of  light  varies  as  the  square 
of  the  distance.  For  instance,  if  the  exposure  is 
known  with  the  light  4  ft.  from  the  subject  and  one 
wishes  to  compute  the  exposure  for  a  distance  of  8 
ft.,  it  is  not  twice  but  four  times  (the  square  of  2, 
the  doubled  distance). 

As  a  basis  for  experiment,  the  following  data  may 
be  of  use:  Subject  6  ft.  from  lens,  and  light  (a  60- 
watt  Mazda)  also  6  ft.  from  subject,  with  ortho  plate 
of  class  ij  and  stop  /:8;  white  reflectors  used;  an 
exposure  of  about  J  to  I  minute  should  be  tried. 
With  two  lamps,  approximately  half  the  exposure 
could  be  given.  The  best  combination  would  be  a 
loo-watt  as  the  principal  and  a  60- watt  as  the  second- 
ary source  of  light.  While  there  may  be  a  little 


62  THE  SECRET   OF   EXPOSURE. 

difficulty  in  determining  the  exposure  by  a  given 
artificial  light,  once  found  it  is  known  for  good,  except 
for  slight  changes  due  to  deterioration  of  the  lamps. 
Cooper-Hewitt  and  other  electric  studio  lights  are 
therefore  economical  of  material,  as  well  as  available 
at  all  seasons. 

Artificial-light  Hints.  —  Frank  W.  Palmer,  who 
has  made  a  specialty  of  the  use  of  Mazda  lamps  in 
portraiture  and  commercial  photography,  kindly  fur- 
nishes the  following  data.  Great  care  is  necessary  in 
the  lighting  and  particularly  in  the  arrangement  of 
reflectors,  to  avoid  harsh  results.  Dead  shadows 
cannot  be  lightened  by  excessive  exposure,  but  only 
by  the  proper  use  of  reflected  light  to  modify  them. 

Using  a  loo-watt  Mazda  about  5  ft.  from  the 
sitter,  with  white  background  and  white  reflector, 
stop/:6,  and  a  Cramer  Inst.  Iso  D.  C.  plate,  15  seconds 
was  found  sufficient.  Another  subject  was  made  with 
a  4O-watt  lamp  shaded  by  one  sheet  of  white  tissue 
paper  and  placed  2\  ft.  from  the  head,  white  reflector 
used  on  the  shadow  side,  and  an  exposure  of  i|  seconds 
given  at  /:5-5  on  the  same  plate.  Both  were  fairly 
well  timed,  and,  though  thin,  print  well  on  soft  D.  O.  P. 

Flowers  have  given  good  results  with  a  60- watt 
lamp  about  2  ft.  above  and  6  ins.  in  front  of  the 
group.  A  sheet  of  white  cardboard  was  set  slanting 
in  front  of  the  group  to  reflect  the  light  up,  and  two 
sheets  of  light  gray  card  were  used  at  the  sides.  An 
exposure  of  40  seconds  at/:6.3  gave  an  excellent  result. 

For  still-life  studies,  the  light  should  be  far  enough 
away  to  insure  an  even  glow  of  light  over  the  entire 
group.  For  example,  a  group  2  ft.  wide  should 
have  the  light  at  least  4  ft.  away  from  the  nearest 


THE   SECRET   OF   EXPOSURE.  63 

point,  and  the  exposure  in  this  case  would  be  about 
3  minutes  with  a  6owatt  lamp  shaded  with  one  sheet 
of  tissue  paper  to  secure  diffusion.  The  reflector 
should  be  managed  so  as  just  to  bring  out  the  outlines 
on  the  shadow  side. 

Flashlight  Exposures.  —  The  following  data  will 
prove  of  value  when  determining  the  amount  of  flash- 
powder  to  use  for  different  distances. 

Plate,  class  ij  color-sensitive;  stop, /:8;  distances 
as  follows: 

6  feet  . . 15  grains 

12  feet 40  grains 

24  feet 105  grains 

36  feet 180  grains 

If  pure  magnesium  powder  is  used  instead  of  the  com- 
pound powder,  take  three  times  as  much. 

Real  Moonlight  Pictures.  —  When  the  moon  is  full 
and  high  in  the  sky  an  exposure  of  30  minutes  at/:8  on 
a  class  i  J  film  or  plate  will  give,  on  an  open  landscape, 
a  picture  which  cannot  be  distinguished  from  a  day- 
light exposure  except  that  there  are  no  cast  shadows. 
This  affords  the  possibility  of  getting  full  detail  on  the 
northern  side  of  objects  without  overexposing  eastern 
or  western  faces.  This  is  sometimes  impossible  by 
daylight.  Such  exposures,  however,  do  not  give  the 
true  moonlight  effect,  and  about  20  minutes  should 
seldom  be  exceeded.  The  disc  of  the  moon  itself  may 
be  registered  in  \  second;  and,  as  it  moves  rapidly, 
will  show  as  an  ellipse  if  given  more  than  2  seconds. 

Shutter  Speeds  for  Moving  Objects.  —  These 
figures  do  not  indicate  the  correct  exposure  for  the 
plate,  but  simply  the  slowest  speed  which  will  give  a 
sharp  image.  Object  distance  25  ft.  from  lens  of  5-in. 
focus  and  moving  diagonally, 


64  THE  SECRET   OF   EXPOSURE. 


People  walking  in  street  scenes .  .  .  . 
Animals  and  people  walking  slowly. 
People  walking  three  miles  per  hour , 
People  walking  four  miles  per  hour . 
Vehicles  at  eight  miles  per  hour.  .  .  . 

Vehicles  at  ten  miles  per  hour 

Vehicles  at  twelve  miles  per  hour .  .  . 

Bicycle  and  horse  races 

High  diving 

Automobile  and  fast  horse  races  . 


Seconds 
-IO 

-25 
-50 
-100 

-150 

-200 
-250 
-500 
-600 
-1000 


If  the  object  is  50  ft.  distant,  twice  as  much  ex- 
posure can  be  given;  and  at  100  ft.,  four  times  as 
much.  The  longer  the  focus  of  the  lens,  the  shorter 
must  be  the  exposure. 

Photographing  from  Moving  Trains.  —  Many  ama- 
teurs like  to  take  pictures  from  the  observation  plat- 
form of  a  train.  This  kind  of  photography  is  the 
reverse  of  ordinary  speed  work,  but  the  same  princi- 
ples apply.  Regardless  of  the  proper  exposure  for  the 
shadows,  one  must  use  a  shutter  speed  high  enough  to 
prevent  blur.  For  pictures  directly  in  the  rear,  an 
ordinary  shutter  will  answer.  The  focal-plane  shutter 
is  efficient  for  angles  up  to  45  degrees,  but  it  cannot 
secure  pictures  at  right  angles  without  distortion,  if 
the  train  is  moving  fast.  Between-lens  shutters 
working  at  1—250  are  capable  of  making  good  pictures. 

Night  Photography.  —  Exposures  suggested  for  trial 
at/:8,  with  ortho  plates  of  speed  ij: 

Minutes 

Lighted  show  windows I 

Illuminated  buildings 2 

Open  streets  with  arc  lamps 3 

The  same,  with  wet  roadway  or  snow 2 

Close  street  scenes 6 

The  same,  with  wet  roadway  or  snow 4 


THE  SECRET  OF  EXPOSURE.  65 

Exposures  for  Interiors.  —  Cover  the  camera  and 
head  with  an  opaque  cloth  and  wait  until  the  eyes  are 
fully  accustomed  to  the  dull  light.  Stop  down  until 
detail  can  barely  be  seen  in  the  deepest  shadow  in 
which  you  wish  to  render  full  detail.  Note  the  stop 
and  consult  the  following  table  for  the  exposure  at 
/:i6  of  a  plate  or  film  classed  as  ij: 


Stop  noted 
/:8        
f:ii 

Exposure  at/:i6. 
56    minutes. 
28    minutes 

/:i6 

14    minutes. 

f-22 

7    minutes. 

/:32 

3^  minutes. 

/'45 

if  minutes 

f:64. 

52    seconds. 

For  other  stops  or  plates,  calculate  from  the  known 
speeds,  remembering  that  each  step  in  plate-speed 
factors  represents  50  per  cent,  whereas  each  listed  stop 
represents  106  per  cent  variation. 

Summary.  —  The  Tables,  when  once  checked  by 
test,  are  remarkably  reliable  as  an  indicator  of  the 
correct  exposure.  Variations  from  them  may  be 
made  if  the  experience  and  judgment  of  the  user 
dictate.  Like  everything  else,  they  work  best  when 
used  intelligently.  When  they  fail,  it  is  because  no 
tables  can  accurately  point  out  the  precise  actinic 
strength  of  the  light  at  the  moment  of  exposure.  The 
only  thing  which  can  do  this  is  an  actinometer. 

Exposure-Meters.  —  The  actinometer  exposure- 
meter  is  the  one  instrument  which  accurately  measures 
the  strength  of  the  light  falling  upon  the  subject.  The 
user  of  this  device  is  not  obliged  to  pay  much  attention 
to  classification  of  subject,  as  he  did  in  the  case  of  the 
Tables.  The  meter  is  the  invention  of  Mr.  Alfred 


66  THE   SECRET   OF   EXPOSURE. 

Watkins,  and  we  cannot  do  better  than  quote  from  The 
Watkins  Manual  what  he  says  on  this  topic. 

"If  the  unobscured  sun  rays  always  fell  on  the 
subject  to  be  photographed,  a  simple  exposure  table 
would  be  a  complete  guide  to  the  variation  of  light. 
But  the  altitude  of  the  sun  is  only  one  influence  affect- 
ing daylight,  there  being  two  classes  of  obstructions 
which  interfere  with  the  light  falling  upon  the  subject. 
These  are:  first,  Clouds  and  Atmosphere;  second, 
Physical  Obstructions. 

"  Clouds  and  Atmosphere.  —  Clouds  between  the 
sun  and  the  earth  obstruct  light,  and  that  in  pro- 
portion to  the  density  of  the  clouds;  hence  we  speak 
of  the  day  being  dull  or  very  dull.  But  clouds  also 
act  as  reflectors,  and  on  many  days  when  the  sun  is 
obstructed,  they  are  thus  secondary  sources  of  light. 
Probably  the  most  brilliant  days  in  summer  are  those 
in  which  the  sun  shines  at  intervals  between  white 
fleecy  clouds,  and  an  object  receives  both  the  unob- 
structed sun  rays  and  also  light  reflected  by  white 
clouds  from  every  part  of  the  dome  of  the  sky. 

"  At  times  vapor  or  fog  in  the  atmosphere  greatly 
alters  the  color  of  the  light  and  lessens  its  chemical 
or  photographic  force.  Such  a  change  is  difficult  to 
detect  by  eye,  which  can  estimate  only  brightness  and 
not  chemical  or,  as  it  is  called,  actinic  force. 

"  Physical  Obstructions.  —  An  object  set  out  in  an 
open  plain  with  the  whole  dome  of  sky  illuminating 
it  receives  the  maximum  amount  of  light.  Anything 
in  the  way  of  trees,  buildings,  roof,  wall,  or  mountain 
which  cuts  off  any  part  of  the  sky  reduces  the  light  and 
tends  to  increase  the  exposure  required.  This  is  a 
far  more  important  influence  than  might  be  supposed. 


THE   SECRET   OF   EXPOSURE.  67 

Let  us  suppose  a  wall  is  built  on  one  side  of  the  subject, 
and  almost  half  of  the  light  is  obstructed.  (We  are 
presuming  that  the  sun  is  not  shining.) 

"  Let  another  wall  be  built  on  the  other  side  of  the 
subject,  which  is  now  illuminated  only  by  a  narrow 
strip  of  sky,  and  the  light  proportionately  lessened. 
This  explains  why  instantaneous  work  in  streets  is 
not  always  so  successful  as  in  open  country. 

"  Now  presume  that  a  roof  has  been  built  over  the 
walls,  and  the  only  illumination  reaching  the  subject 
comes  through  a  window.  The  volume  of  light  is  now 
enormously  lessened,  and  to  secure  a  correct  exposure 
probably  two  or  three  hundred  times  the  exposure 
must  be  given  for  that  required  under  the  conditions 
of  the  first  example. 

"It  will  now  be  seen  why  views  under  trees,  near 
buildings,  on  porches  and  indoors  require  much  longer 
exposures  than  open  landscapes.  .  .  .  Fortunately, 
a  test  with  a  simple  instrument  called  an  actinom- 
eter  will  accurately  give  the  value  of  the  light  which 
falls  upon  the  subject,  and  one  test  will  allow  for  month, 
time  of  day,  clouds  and  atmosphere,  and  physical  ob- 
structions caused  by  the  variation  of  subject.  The 
actinometer  (or  exposure-meter,  as  it  is  called  when 
combined  with  scales)  has  a  disc  of  paper  which  is  sen- 
sitive to  the  same  kind  of  light  as  the  sensitive  plate. 
This  paper  darkens  alongside  a  painted  standard  tint, 
and  it  is  found  by  experience  that  the  time  required 
for  darkening  to  the  standard  tint  indicates  accurately 
the  photographic  power  of  the  light  illuminating  the 
subject.  .  .  .  There  are  many  reasons  why  a 
simple  actinometer  test  is  more  reliable  than  judging 
the  value  of  the  light  by  the  eye.  One  is  that  light 


68  THE   SECRET   OF   EXPOSURE. 

which  has  a  yellow  tinge  (as  towards  sunset  or  in  fog 
or  east  winds)  may  appear  visually  bright,  but  is 
actinically  (or  chemically)  feeble.  Another  reason  is 
that  the  pupil  of  the  eye  automatically  accommodates 
itself  to  different  degrees  of  light.  We  pass  from  the 
open  air  into  a  room  which  we  call  well  lighted,  and 
the  eye  does  not  give  much  information  as  to  the 
enormous  difference  between  the  light  in  and  out  of 
doors;  probably  one  to  one  hundred.  The  actinom- 
eter  will  give  it  with  fair  accuracy. 

"  In  my  system  of  exposure,  therefore  (which  was 
original  when  introduced  by  me,  although  copied 
since),  the  keynote  to  the  whole  plan,  and  the  golden 
rule  is  to 

"Test  the  Light  which  Falls  upon  the  Subject, 
and  this  rule  applies  to  practically  all  cases  in  which 
a  camera  is  used,  and  even  for  copying,  enlarging,  and 
photomicrographs  where  a  condenser  is  not  used.  The 
standard  for  the  actinometer  is  that  it  darkens  to  its 
standard  tint  in  best  light  (that  is,  unclouded  mid-day 
summer  sunshine  in  England)  in  two  seconds,  and  the 
darkening  time  in  less  active  light  will  be  in  direct 
proportion  to  the  altered  time  of  exposure  required. 
It  will  be  seen,  therefore,  that  this  one  test 
with  the  actinometer  fully  allows  for  all  the  variations 
which  the  exposure- tables  classify  as  month,  time  of 
year,  time  of  day,  state  of  atmosphere  and  (to  a  great 
extent)  subject." 

Exposure-Meters.  —  The  two  standard  meters  are 
the  Watkins  Bee  Meter  and  the  Wynne  Infallible. 
Both  are  made  in  watch  form  and  supplied  for  use  with 
either  /  or  Uniform  System  (U.  S.)  stops. 

The  Watkins  meter  is  cheaper  and  has  only  one 


THE   SECRET   OF   EXPOSURE.  69 

series  of  plate-speed  numbers;  the  Wynne  costs  more 
and  uses  /  numbers  or  U.  S.  numbers  to  denote  the 
speed  of  the  plates;  the  Watkins  has  a  slower  paper 
(or  darker  standard  tint)  and  requires  four  times  as 
long  as  the  Wynne  to  make  the  actinometer  test.  In 
the  Watkins  instrument  the  stop  number  is  set  against 
the  plate-speed  number,  and  hence  the  scales  do  not 
have  to  be  moved  as  long  as  the  same  stop  is  in  use. 
The  Wynne,  on  the  contrary,  requires  resetting  every 
time  the  light  value  changes,  though  the  correct  ex- 
posures for  all  the  stops  may  be  read  as  soon  as  the 
light  value  has  been  set  against  the  plate  speed  num- 
ber. Mr.  Watkins'  latest  pattern,  the  Focal  Plane 
meter,  is  arranged  like  the  Wynne.  It  indicates  half 
the  exposure  of  the  Bee  pattern,  as  it  is  designed 
primarily  for  snapshots.  The  Wynne  Snap  Shot 
meter  is  similar.  There  is  really  very  little  to  choose 
between  them,  as  some  workers  prefer  one  and  some 
the  other.  As,  however,  we  have  used  the  Watkins 
meter  longer,  we  shall  confine  our  remarks  to  our 
experience  with  it. 

The  first  thing  to  learn  in  using  a  meter  is  to  match 
the  tint  by  its  darkness,  not  by  its  color.  That  is, 
the  paper  must  be  exposed  until  it  looks  as  deep  a 
shade  as  the  standard  tint.  A  blue  glass  dial  is  a 
great  help  in  preventing  the  tendency  to  match  color 
instead  of  darkness.  The  length  of  time  should  be 
noted  by  the  watch  or  by  the  swinging  of  a  half-second 
pendulum. 

The  second  thing  is  to  select  the  correct  plate 
number  to  use.  Suppose  you  are  using  a  film  which 
is  listed  on  the  Watkins  speed  card  as  90.  Take  the 
light  value  or  actinometer  time.  Suppose  it  to  be 


70  THE   SECRET   OF   EXPOSURE. 

four  seconds.  Set  /:8  (in  column  over  "  stop  ") 
against  90  (on  the  rim  of  the  meter).  Then  against 
4  (in  column  over  "  light  ")  will  be  found  22,  which 
means  1-22  second.  Give  1-25  second  at  /:8  on  an 
average  landscape.  Now  calculate  with  plate  num- 
bers of  130  and  1 80,  and  give  respectively  1-32  and 
1—45  second.  The  best  way  to  manage  this  is  to  use 
the  same  speed  of  the  shutter  and  stop  down  to  halfway 
between /:8  and/:ii  for  the  1-32  and  to/:ii  for  the 
1-45  second.  When  these  exposures  are  developed 
together  for  the  same  length  of  time,  it  will  be  easy  to 
pick  out  the  one  which  gives  the  best  print.  Possibly 
an  even  higher  plate  number,  as  250,  might  give  pass- 
able exposure  for  snapshot  work. 

Using  the  Quarter  Tint.  —  We  have  often  found  it 
more  convenient  to  take  the  time  it  requires  to  darken 
the  paper  to  the  quarter  tint,  multiplying  this  by  2 
to  obtain  the  actinometer  time  for  calculation,  as  we 
find  the  full  meter  time  is  rather  more  than  is  neces- 
sary, and  our  standard  outdoor  exposure  is  therefore 
half  the  Bee  meter  time,  or  exactly  the  Focal  Plane 
meter  time.  In  very  good  light,  we  use  the  darker,  or 
standard  tint,  and  calculate  with  half  the  number 
of  seconds,  which  amounts  to  the  same  thing.  The 
Watkins  meters  are  now  regularly  furnished  with  only 
one  tint,  the  standard.  In  using  the  Wynne  meter, 
however,  we  find  it  difficult  to  judge  the  lighter  tint, 
and  use  only  the  darker  or  standard  tint,  which  re- 
quires by  actual  tests  about  the  same  time  as  the  Wat- 
kins  quarter  tint.  The  first  visible  darkening  of  the 
paper  in  the  Watkins  meter  takes  place  in  one-sixteenth 
of  the  full  actinometer  time;  hence  this  value  may  be 
used  in  dull  light  or  indoors  to  shorten  operations. 


THE   SECRET   OFt  EXPOSURE;  -  > '-''it'- 

What  Light  to  Test.  —  As  a  general  rule,  we  find  it 
advisable  to  counteract  the  tendency  of  the  meter 
to  indicate  exposures  which  are  unnecessarily  great 
by  testing  the  direct  sunlight.  The  instructions  (for 
Boston  conditions  outdoors,  at  any  rate)  should  read: 

Take  sunlight  for  all  average  subjects.  Where  full 
detail  is  wanted  in  shadows  near  the  camera  in  outdoor 
work,  the  meter  should  point  to  the  sky  in  a  direction 
at  right  angles  to  the  sun's  rays,  which  should  not  fall 
upon  the  paper. 

For  dark,  heavy  foregrounds,  expose  the  paper  in 
the  shade  of  the  body. 

Always  hold  the  meter  to  face  the  light  which  falls 
upon  the  subject,  not  to  face  the  subject. 

An  Alternative  Plan.  —  Lately,  instead  of  using  a 
higher  plate  number,  we  have  been  taking  the  published 
figures  and  using  J  the  time  required  for  matching  the 
full  tint  in  calculating  for  snapshot  exposures  in  hand 
camera  work.  We  find  that  we  thus  get  full  exposure 
and  a  soft,  quick-printing  negative;  but  our  shutter 
speeds  are  tested  and  the  efficiency  is  high,  as  it  is  an 
expensive  modern  shutter. 

These  are  really  the  only  stumbling  blocks  which 
need  to  be  removed  in  order  to  make  the  use  of  the 
meter  easy  and  dependable.  If  you  use  a  few  films 
and  thereby  settle  on  a  plate  number  which  gives 
just  the  sort  of  negative  you  wish,  there  will  be  no 
chance  of  overexposure.  The  actinometer  test  is  a 
strictly  accurate  measure  of  the  actinic  strength  of 
the  light.  One  afternoon  in  October  at  3.10  P.M.  we 
tested  the  light  and  got  a  full  tint  in  sunlight  in  8 
seconds.  Fifteen  minutes  later  it  took  45  seconds  — 
nearly  six  times  as  slow,  or  the  difference  between 


OF  EXPOSURE. 

exposures  of  1—25  and  1—5.  The  eye  could  not  dis- 
tinguish any  difference,  but  a  plate  given  1-25  would 
have  been  hopelessly  undertimed  at  3.25  P.M.  No 
table  could  have  measured  this  difference  accurately. 
Hence  the  worker  who  aims  at  the  best  results  from 
every  exposure  should  learn  to  use  a  meter  and  fall 
back  upon  it  when  in  doubt. 

Prism  Meters.  —  A  form  of  exposure  meter  which 
is  much  liked  by  those  who  have  become  used  to  it  is 
typified  by  the  Heyde.  In  this  instrument,  blue- 
glass  prisms  are  used  to  cut  out  the  light  reflected  from 
the  object.  One  looks  through  the  eyepiece  and  turns 
the  thicker  portion  of  the  prisms  (one  or  both,  accord- 
ing to  the  luminosity  of  the  object)  into  position  until 
the  shadow  details  are  suppressed.  By  reference  to 
Tables,  the  necessary  exposure  may  readily  be  found. 
Like  all  other  devices  of  this  nature,  such  an  optical 
apparatus  requires  considerable  adaptation  to  the 
user's  personal  equation,  because  the  eye  ordinarily 
can  be  made  to  accommodate  sufficiently  to  accept  as 
correct  any  one  of  a  number  of  positions  of  the  prisms, 
if  viewed  long  enough.  The  user  has  therefore  to  try 
several  positions  in  rapid  succession  until  it  becomes 
evident  that  a  certain  one  does  cut  out  the  shadow 
details,  whether  compared  to  a  lighter  or  to  a  darker 
portion.  Once  the  knack  is  mastered,  though,  the 
user  finds  a  Heyde  meter  very  reliable  and  rapid  in 
action. 


Proper  Material, 

carefully  selected,  should  be  the  basis  of  your 

photographic  beginning. 
Let  us  aid  you  from  our  large  stocks  of  dependable 

equipment. 
The  leading  house  of  New  England  for  high 

grade  apparatus. 

Correspondence  and  enquiries  solicited. 
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"  SEMI-ACHROMATIC  " 

PINKHAM  &  SMITH   COMPANY 


TWO  STOKES 


BOSTON,  MAS, 


NOT   MERELY   Jt   SUBSTITUTE    FOR   SUNLIGHT,    BUT 
THE    SUBSTITUTE;     THE    ONLY    ARTIFICIAL    LIGHT 

THAT    IS 

"BETTER  THAN  DAYLIGHT" 

FOR      MLL      PHOTOGRAPHIC 
PURPOSES— 

THAT'S  COOPER  HEWITT  LIGHT 

Cheaper  than  daylight,  too,  because  you 
can  turn  out  more  work.  Isn't  your  energy 
worth  more  than  electric  energy  ? 

Quality  portraits  are  produced  by  Cooper 
Hewitt  light,  — gives  modeling  and  atmos- 
phere to  a  subject  that  is  only  occasionally 
hit  upon  with  sunlight,  because  Cooper 
Hewitt  is  so  much  more  manageable. 

Progressive  photographers  are  naturally 
investigating  the  Cooper  Hewitt  Light. 

Write  for  new  Catalogue  No.  C  4958. 


Cooper  Hewitt  Photo 


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Eighth  &  Grand  Streets 

Hoboken,   N.  J. 


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CONCERNING 

PRACTICAL  PHOTOGRAPHY 

FROM  THE  PUBLISHER  TO  THE  READER 


A  study  of  this  number  of  Practical  Photography  will  show  you  the  aim  of  the  series,  which 
is  to  give  in  each  number  all  of  the  necessary  information  for  a  mastery  of  some  small  part 
of  the  domain  of  photography.  It  is  not  the  intention  of  the  Editors  to  include  a  lot  of  use- 
less theories,  but  each  number  will  reflect  the  present  state  of  our  knowledge  of  some  branch 
of  photography,  plainly  told  in  such  a  way  that  the  knowledge  can  be  immediately  put  into 
practice  in  the  workroom  or  the  field.  Each  book  will  be  illustrated  as  liberally  as  a  com- 
plete understanding  of  the  subject  demands,  but  no  pictures  will  be  introduced  merely  be- 
cause of  their  beauty,  or  because  of  their  artistic  value.  The  books  will  be  well  made  from 
the  standpoint  of  typography,  paper,  and  illustrations,  will  be  sewed  to  open  flat,  and  will 
handily  fit  the  pocket.  They  will  be  issued  in  two  bindings,  paper  and  cloth.  The  paper 
edition  will  cost  twenty -five  cents  per  issue,  or  $2.50  by  subscription  for  twelve  numbers. 
The  price  of  the  cloth  edition  will  be  fifty  cents  a  copy,  or  $5.00  for  twelve  numbers.  Some 
description  of  the  first  three  numbers  follows. 

NO.   i.    "THE  SECRET  OF  EXPOSURE." 

If  exposure  is  correct,  all  other  steps  in  the  making  of  a  good  negative  are  merely  mechan- 
ical. This  book  contains  a  complete  system  for  obtaining  correct  exposure,  on  all  occasions. 
It  discusses  all  the  factors  governing  exposure,  all  the  conditions  under  which  it  should  be 
made,  and  gives  full  and  explicit  directions  for  obtaining  correct  exposure  under  all  circum- 
stances. Complete  exposure  tables  and  speed  lists  of  all  plates  on  the  American  market 
are  given,  and  the  book  concludes  with  a  clear  discussion  of  the  use  of  exposure  meters.  It 
is  the  most  complete  and  practical  treatise  on  exposure  ever  written. 

NO.  2.    "BEGINNERS'  TROUBLES." 

Though  this  book  would  seem  to  be  intended  only  for  the  novice  in  photography,  it  con- 
tains an  enormous  number  of  practical  hints  of  value  to  every  practitioner.  In  a  way  it  is 
a  manual  of  photographic  work,  for  it  gives  useful  pointers  for  success  in  all  the  departments 
of  photography  for  making  a  perfect  negative  and  a  satisfactory  print  from  it.  Its  primary 
purpose  is  to  show  what  may  be  the  causes  of  failure,  and  to  help  the  reader  to  avoid  these 
causes. 

NO.  3.    "HOW  TO  CHOOSE  AND  USE  A  LENS." 

Without  being  too  theoretical,  this  book  explains  the  reason  for  existence  and  the  partic- 
ular qualities  of  each  type  of  lens  now  in  use  in  photography.  It  tells  exactly  what  each 
will  do,  and  how  it  may  be  used  to  the  best  advantage.  It  particularly  describes  the  more 
modern  varieties  of  lenses,  and  gives  full  information  as  to  the  differences  between  them. 
It  tells  how  to  test  a  lens,  and  answers  many  questions  which  every  user  of  a  lens  is  sure  to 
ask. 


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AMERICAN   PHOTOGRAPHIC   PUBLISHING   CO. 
221    COLUMBUS   AVENUE,   BOSTON,    MASS. 

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M 


THE  ELEMENT  OF  TIME 

is  the  prominent  factor  in  photography  to-day.  There  is  more  wastage  from  insufficient 
exposure  or  movement  on  the  part  of  the  subject,  than  occurs  from  any  other  cause  in  the 
process. 

A  &  H  Record  Plates  enable  you  to  make  snap-shots  in  the  house,  and  short  time 
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WYNNE'S  INFALLIBLE  HUNTER  METER 

The  Wynne's  Infallible  Hunter  Meter  has  been  specially  designed  to  attain  the  maxi- 
mum of  simplicity,  convenience  and  efficiency,  with  a  minimum  diameter,  and  thickness  of 
case  —  the  case  being  only  one-quarter  of  an  inch  in  thickness.  It  is  beautifully  made  in 
the  best  Solid  Nickel  and  opens  automatically  by  pressure  of  the  small  knob  on  the  pendant. 

On  the  right  hand  side  of  the  open 
case  is  the.  Actinometer  with  standard 
tints  and  sensitive  paper.  On  the  left 
hand  side  of  the  case  are  the  two  scales 
for  the  calculation  of  the  exposures.  The 
top  dial  is  interchangeable  so  that  scales 
according  to  either  F,  U  S,  or  specially 
divided  scales  for  Autochrome  exposures 
can  be  instantly  substituted  for  one 
another. 

When  ordering,  please  specify  which  style  of  scale  is  desired. 

$2.75 

25 


Hunter  Meter 

Extra  packages  Sensitive  paper 

Pocket  case  of  tan  leather 

Set  of  top  and  bottom  dials 

Top  Scale  only  F  or  U  S 

Autochrome  Scale  and  instruction  book 

Extra  book  of  instructions 

Extra  speed  card 


•  50 

•  So 

•  25 

•  35 
.10 
.10 


American  Agents:  GEORGE  MURPHY,  Inc. 

57  East  9th  Street,  New  York 

Manufacturers,  Importers  and  Dealers  in  Photographers'  Materials  of  Every  Description. 
Send  for  New  Post-paid  No.  14  Mail-Order  Cash  Catalogue. 


Please  mention  Practical  Photography  when  writing  Advertisers 


EVERY  reader  of  this  book  is  sure  to  be  seriously  interested  in  photography.  This 
being  the  case,  he  should  follow  the  progress  of  the  art,  and  keep  continually  in  touch 
with  its  latest  developments.  The  surest  way  for  him  to  do  this  is  to  subscribe  to  one 
or  more  of  the  photographic  magazines,  and  we  should  be  very  happy,  in  case  he  is  not  ac- 
quainted with  them,  to  send  him  sample  copies  of  our  two  monthlies,  AMERICAN  PHO- 
TOGRAPHY and  POPULAR  PHOTOGRAPHY.  Each  of  these  magazines  is  edited 
with  the  idea  of  giving  each  reader  as  much  help  and  service  as  the  Editors  can  possibly 
furnish.  The  answering  of  perplexing  questions,  the  criticism  of  readers'  pictures,  with  an 
idea  of  showing  how  they  may  be  improved,  the  stimulation  of  effort  by  the  awarding  of 
prizes  in  monthly  contests,  the  furnishing  of  information  as  to  how  the  camera  may  be  made 
a  means  of  pecuniary  help,  are  but  a  few  of  the  manifold  ways  in  which  our  Editors  give 
the  readers  service.  A  more  particular  description  of  the  characteristics  of  the  two  maga- 
zines follows,  but  the  best  way  to  learn  about  them  is  to  send  for  a  sample  copy,  which  will 
cost  you  nothing  and  subject  you  to  no  obligation. 

AMERICAN  PHOTOGRAPHY  is  today  the  standard  American  photographic  magazine, 
and  has  for  years  endeavored  to  follow  its  motto  by  "representing  all  that  its  name  implies." 
It  covers  the  whole  field  of  photography,  for  amateur,  professional  and  commercial  photog- 
rapher, publishing  each  month  numerous  strong  articles  on  the  best  current  practice  and  the 
latest  advances  in  each  of  these  departments.  A  strong  motion  picture  department  is  one 
of  its  specialties;  and  it  continually  endeavors  to  interest  its  readers  in  other  departments 
of  photography  which  will  broaden  their  activities  and  give  them  some  interests  beyond 
the  making  of  ordinary  pictures,  which  may  lose  interest  after  a  while.  Its  departments 
include  "Questions  and  Answers,"  "Practical  Hints,"  "Our  Portfolio"  for  picture  criticism, 
"The  Round  World  Exchange  Club"  for  the  exchange  of  prints,  "The  Market  Place,"  with 
information  as  to  ways  of  selling  pictures,  "Competitions,"  literary  and  pictorial,  "Notes 
and  News"  of  clubs  and  manufacturing  activities.  The  subscription  price  is  $1.50  a  year 
in  the  United  States. 

POPULAR  PHOTOGRAPHY  is  a  magazine  intended  primarily  for  the  less  advanced 
amateur.  While  the  illustrations  of  AMERICAN  PHOTOGRAPHY  come  largely  from 
exhibitions  and  show  the  achievements  of  the  more  distinguished  photographers  of  the  day, 
POPULAR  PHOTOGRAPHY  is  illustrated  solely  from  the  work  of  readers,  of  the  kind 
which  every  amateur  wants  to  take,  and  with  each  print  is  given  a  complete  description  of 
the  exact  method  by  which  it  was  made  and  a  criticism  telling  how  it  might  have  been  im- 
proved; thus  forming  a  guide  whereby  every  reader  can  make  prints  similar  to  those  which 
he  admires  in  the  pages  of  the  magazine.  In  addition  to  these  picture  criticisms,  the  maga- 
zine contains  numerous  short  and  pointed  articles,  most  of  which  are  written  in  response  to 
definite  queries  from  readers  for  information  on  certain  points.  They  thus  reflect  the  needs 
of  the  day,  and  have  proved  extremely  popular.  The  whole  keynote  of  the  magazine  is  to 
be  brief  and  practical,  and  no  long  theoretical  articles  are  published.  It  has  consequently 
proved  very  attractive  to  professional  photographers  as  well  as  the  amateurs  for  whom  it  is 
primarily  designed.  A  monthly  competition  and  some  other  departments  are  run  by  this 
magazine  as  well  as  by  AMERICAN  PHOTOGRAPHY.  The  subscription  price  is  $1.00 
a  year  in  the  United  States. 


AMERICAN   PHOTOGRAPHIC   PUBLISHING   CO. 
440   POPE   BUILDING,   BOSTON,   MASS. 

Please  mention  Practical  Photography  when  writing  Advertisers 


Make  your 

KODAK 


T 


VHE  most  important  photographic  develop- 
ment in  two  decades,  is  the  Autographic 
Kodak.      It   makes  the   record   authentic; 

answers  the  questions :  When  did  I  make  this  ?  Where  was  this 
taken?  Every  negative  worth  taking  is  worth  such  date  and  title. 
With  the  Autographic  Kodak  you  make  the  record,  almost  instantly, 
on  the  film. 

It's  very  simple.  Open  the  door  in  the  back  of  Kodak,  write  the 
desired  data  on  the  red  paper,  expose  for  a  second  or  so,  close  the  door. 
When  the  film  is  developed,  the  records  appear  on  the  intersections 
between  the  negatives. 

This  autographic  feature  having  now  been  incorporated  in  the  most 
important  Kodak  models,  we  have  arranged  to  take  care  of  our  old  cus- 
tomers by  supplying  Autographic  Backs  for  Kodaks  of  these  models. 

The  old  Kodak  can  be  brought  up  to  date  at  small  cost,  and  there 
is  no  extra  charge  for  autographic  film.  Make  your  Kodak  Auto- 
graphic. 

PRICE-LIST  OF  AUTOGRAPHIC  BACKS. 

No.  1  Kodak  Junior,         .       .       .    $2.50  No.  *  Folding  Pocket  Kodak,  .  $4.00 

No.  1A  Kodak  Junior,      .        .        .3.00  No.  4A  Folding-  Kodak,       .  .  4.50 

No.  1A  Folding  Pocket  Kodak,  R.  No.  1A  Special  Kodak,         .  .  4.00 

R.  Type 3.50  No.  3  Special  Kodak,            .  .  4.00 

No.  3  Folding:  Pocket  Kodak,         .      3.50  No.  3A  Special  Kodak,         .  .  4.26 
No.  3A  Folding  Pocket  Kodak,     .     3.75 

Catalogue  free  at  your  dealer's,  or  by  mail. 

EASTMAN  KODAK  COMPANY,  ROCHESTER,  N.  Y. 


Please  mention  Practical  Photography  when  writing  Advertisers 


Almost  another  camera 
for  fifty  cents. 


The  regular  Kodak  lens  equipment  brings  you 
six  feet  from  your  subject 

The  Kodak  Portrait  Attachment 

slipped  on  over  the  regular  lens,  brings  you  as 
near  as  2  ft.  8  inches  unless  you  are  working  with 
a  fixed  focus  Kodak  or  Brownie  when  3^  ft., 
an  ideal  distance,  by  the  way,  for  portraiture, 
becomes  the  shortest  range. 

By  reason  of  this  decreased  distance,  you  may 
take  head  and  shoulder  portraits  of  good  propor- 
tions, pictures  of  household  pets,  flowers,  favorite 
articles  of  furniture — heirlooms  perhaps,  that, 
with  the  regular  lens  equipment,  would  appear 
too  small  in  the  print  to  give  the  desired  effect. 

And  for  fifty  cents. 

EASTMAN  KODAK  COMPANY, 
ROCHESTER,  N.  Y. 

At  your  dealer'*. 

Please  mention  Practical  Photography  when  writing  Advertisers 


The  Kodak  Film  Tank 

has  made  the  amateur's  dark- 
room a  relic  and  better  negatives 
the  rule. 

As  far  as  film  development  goes, 
the  veriest  novice  is  the  equal  of 
the  expert — from  the  start. 

The  Experience  is  in  the  Tank. 


EASTMAN  KODAK  COMPANY, 

ROCHESTER,  N.  Y. 


At  your  dealer'*. 


Please  mention  Practical  Photography  when  writing  Advertisers 


The  large  print 
The  easy  way 

with  the 

Vest  Pocket 
Kodak  or 
Brownie 
Enlarging 
Camera 


Some  of  your  better  pictures  will  have  an  added  charm,  a 
freshened  interest  in  the  enlargement,  and  with  no  loss  of  detail. 

To  secure  large  prints  with  the  Vest  Pocket  Kodak  or  Brownie 
Enlarging  Camera  is  simply  a  matter  of  moments,  not  of  ability. 
Just  slip  in  your  Velox  paper  at  the  large  end  of  the  camera,  your 
negative  in  at  the  other,  expose  to  daylight  and  develop  and  fix 
in  the  regular  way. 

No  focusing — no  dark-room. 


THE  PRICE. 

V.  P.  Kodak  Enlarging-  Camera,  for  3}£  x  5K  enlargements  from  \%  x  2%  negatives, 
No.  2  Brownie  Post  Card  Enlarging  Camera,  for  3M  x  5M  enlargements  from  2K  x 

3K  negatives, - 

No.  2  Brownie  Enlarging  Camera,  for  5x7  enlargements  from  2%  x  3)£  negatives,  - 
No.  3  Ditto,  for  6K  x  8K  enlargements,  from  3K  x  ±%  negatives,  -  -  -  -  - 
No.  4  Ditto,  for  8  x  10  enlargements,  from  4x5  negatives  (will  also  take  3%  x  5^ 

negatives),       ....--.--------- 

EASTMAN  KODAK  COMPANY, 
ROCHESTER,  N.  Y. 

At  your  dealer's. 


$1.75 

1.75 
2.00 
3.00 


Please  mention  Practical  Photography  when  writing  Advertisers 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


! 


AN  INITIAL  FINE  OP  25  CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $I.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


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